GURPS Dungeons and Dragons
A Dungeons and Dragons to GURPS conversion has been taking shape under the efforts of Ontological Zombie. His general aim has been to capture the feeling and flavor of playing Dungeons and Dragons in GURPS, rather than to work out a simple straight conversion. GURPS Martial Arts and GURPS Magic are both highly recommended; GURPS Fantasy and GURPS Banestorm are not strictly needed but may offer some inspiration.
While occupational templates are helpful and racial templates very useful, GURPS players should not feel that they need to shoehorn their characters into DnD classes in order to capture the feeling of the genre. A strong focus is helpful for any character, but one should always play to the strengths of the system being utilized. It is recommended that one chooses a focus for every character... one or two things the character excels at (combat, magic, sneakiness, social interaction, investigation) based on what sort of things you, as a player, enjoy having your character do.
A 100 point character emulates a first level dungeons and dragons character fairly well when it comes to relative power level. This enables a player to create a talented beginner with no experience. Beyond first level, adding 25 character points per level dedicated to the character's focus. A character with a combat focus might add to combat skills and advantages, while a magic focused character might improve spells and fatigue. Since this conversion also recommends a gradual increase in cinematic rules as the overall party level increases, more and more cinematic skills and advantages become available.
Attribute Modifiers: HT+1 
Secondary Attribute Modifiers: Basic Move-1 [-5]
Advantages: Extended Lifespan 1, Longevity , Resistant to Poison +3 , Magic Resistance +3 , Infrared Vision 
Disadvantages: Stubbornness [-5]
Attribute Modifiers: DX+1 ; HT-1 [-10]
Advantages: Unaging ; Infrared Vision ; Acute Vision +2 ; Silence 1 ; +8 Resistance to Sleep/Charm spells
Features: Racial skill bonuses: Bow+1 ; Shortsword+1 ; Broadsword+1 
Secondary Attribute Modifiers: Size -1; Basic Move -1[-5]
Advantages: Magic Resistance +3 ; Speak with Burrowing Mammals ; Infrared Vision 
Advantages: +3 vs sleep/charm spells , Infrared Vision , Acute Vision +2
Attribute Modifiers: DX +1; ST -1[-10]
Secondary Attribute Modifiers: Size -1; Basic Move -1[-5]
Advantages: Resist Poison +3 ; Resist Magic +3 ; Silence 1 
Attribute Modifiers: ST +1; HT +1
Advantages: Infravision 
Disadvantages: Ugly [-8]
Until and unless comprehensive spell lists have been written up, the GM and players should work together to decide which spells work as arcane, and which would be provided under a given deity's Power Investiture. Dungeons and Dragons spell memorization system was a form of game balance, and unless a GM feels like hacking out a Vancian remember/forget GURPS magic system, can be safely ignored.
Likewise it is perfectly fine to just use the standard GURPS spells rather than convert from Dungeons and Dragons. However, because GURPS spells only real balance are their prerequisites, if a GM wanted to do such a conversion, it is reccomended that he work up prerequisite trees for them as he does so, with one or two prereqs per level of spell. It is worth noting that this will significantly make even weak wizards much more powerful due to the nature of DnD damage spells and GURPS combat.
A simpler way to convert DnD's magic system might be to simply add a Caster Level unusual background, and let GURPS characters use the DnD rules when casting spells. This is also likely to be hideously unbalanced due to the differences in DnD and GURPS hit points.
A final option for Magic might be to simply use "GURPS Powers" for all spells, using them as advantages.
In addition to Power Investiture and True Faith, devout characters might be allowed to purchase abilities from GURPS Powers to represent things like Laying on Hands, Holy Auras, or whatever a particular deity might gift a mortal follower with. This might augument or even replace a clerical spell system.
The style and optional rules used will have a tremendous impact upon the game. At low levels (100 to 200 points or so) players will feel vulnerable, threatened, and the ruleset should reflect this perceived vulnerability. At higher levels (500-600 points) the game is essentially Fantasy Superheroes, and the rules should be far more relaxed. Below are some recommended rules thresholds.
At 100 to 200 character points the characters are at their most vulnerable, but the game is still cinematic. The following optional rules form that which is referred to as Borderline Realism in GURPS Martial Arts.
- "Buying Successes" (p. B347)
- "Extra Effort in Combat" (p. B357)
- "Dual-Weapon Attacks" (p. B417)
- "All Out Attack (Long)" (p. MA97-98)
- "Committed Attack" (p. MA99-100)
- "Defensive Attack" (p. MA100)
- "Acrobatic Movement" (p. MA105-107)
- "Acrobatic Attack" (p. MA107)
- "Quick Shooting Bows" (p. MA 119-120)
- "Tricky Shooting" (p. MA121)
At this stage it's also appropriate to limit character attributes to 20 and enforce the suggested limits on secondary attributes. Limiting skill levels to 25 may also be helpful.
From 200 to 300 characters have gotten their footing and are more able to forge their own destinies, and a more flexible reality is required to contain them. The rules from above are in effect, as well as all of the cinematic rules other than "Chambara Fighting" (p. MA128-130) and "More Cinematic Combat Rules" (p. MA132-133) are in effect. Trained by a Master and Weapon Master are available, extra attacks become feasible.
From 300 to 500 characters are truely epic. Use every Cinematic rule in Martial Arts other than "Bullet Time" (p. MA133) and, if the campaign is not that way, the silly ones.
At 500 plus the characters are virtual demigods, and even a rubber reality cannot cope with their gravitas. They start to become incomprehensible. Any and all cinematic rules are in play, and some of the core rules can be relaxed... the rule of 16, parrying heavy weapons/unarmed, weapon ST requirements... campaigns that last this long are custom jobs, as only their GMs know how to take it from here.