Sollir Furryfoot said:Hrm, what I would do is to separate the major and minor arcana, and use them only during combats. I would assign an effect to each major arcana that befits the card, such as the Fool making all rolls of 1-2 automatic/critical failures and the Magician adding +2 to the caster level of all arcane spells. A card from the minor arcana deck would then be drawn, which would determine the number of rounds the major arcana would last (by their corresponding number), and who it effects (allies, opponents, everyone, or no one/or perhaps/Swords-Fighters/Barbarians/Rangers, Coins-Rogues/Bards, Wands-Wizards/Sorcerers, Cups-Clerics/Druids/Paladins) by its type. Whenever the duration of the card effect would end, then another card in its place would be drawn, until the end of the battle.
Suggestions for the effects of Major Arcana (Note that I only have some knowledge on tarot cards):
I would suggest not to reshuffle until the end of a battle for best results. The main purpose would be to add a little flavor and unpredictability in battle (A normally easy battle may turn disastarous if the Devil or Death or both). Hope that helps. I invented this on the fly, btw, and am seriously considering using it in my own game-probably I'll make a PrC which focuses on influencing the draw's decision in the future if I do so.
A couple things. First, if you want to go with the traditional associations of the suits, Swords would be the suit associated with intellectual classes and wizardry, while Wands is the suit of action and physical power (i.e., warriors).
Second, i'd recommend against using Tarot for the scale of action resolution that D&D3E generally does--it's no real change if you just go with the numbers, and the flavor is either lost or overwhelming if you use it. Instead, Tarot is best used for an RPG if you use a very different style of action resolution than D&D does: larger chunks, first of all (decide whole battles, not individual blows), and more thematic rather than logical in application. Doing this takes advantage of the strengths of the cards (complex variable meanings) while minimizing their flaws (inspecific and a bit more time-consuming than rolling a die).
Oh, and whatever you do, i'd recommend deciding on specific rules for replace-and-reshuffle. Not much point in doing it after every draw--again, it becomes just like a die. Everway has you reshuffle whenever you draw a specific card (Usurper), and you could do the same with a Tarot--or make it every time you draw a Major Arcana. Or you could simply go through the entire deck, and then reshuffle.
What Sollir proposes above would be great as an add-on to D&D (though i think it'd work better as a reflection of a general setting, than attached to just a specific character), but doesn't, IMHO, really take advantage of the cards. It's really just a d22 roll. What sets cards apart from dice is the complex nature of the data encoded. IOW, a die only gives you one piece of data: a number. A card gives you at least 2: number and suit/color. And possibly many more once you deal with something like a Tarot deck. Take advantage of this, and extract multiple bits of data from them for your resolution system. Better yet, take advantage of the variable nature of them: a "17" always has the same meaning on a die, but "The Devil" is open to quite a bit of interpretation. If you then narrow those possibilities down to a single meaning/outcome, i think you've missed the point, and may as well be using dice.