you don't need strobes, just a good tripod with a level, a macro lens (macro lenses have a flat plane of focus, rather than a slightly curved one) 2 lights, point them to the center from 45ยบ, then feather them to the sides, check with a light meter to see that the light is even across the entire piece, use a cable release and mirror lockup if possible, use a polarizing filter to reduce glare/flare, and you should be good to go.
slide film comes in very different types. you could get astia to try and have the colors remain as close to normal as possible. almost all slide films are very slow iso, so having a good tripod etc is a must.
slide films like all films have a issue on longer exposurers, called reciporcity, where the film begins to break down over 1 second, and you end up needed more time to expose correctly for. some are better than others, and you should plan accordingly. something like kodak 64t holds up very well, and is color balanced to work with tungsten lighting.
If he is using strobes, reciprocity won't be an issue.
As for using medium format for slides to project, he will have one hell of a time finding someone that will mount medium format slides. As everyone said, get a 35mm body, the quality of a 35mm will blow your 20D out of the water.
As for film of course i'd use a neutral film such as sensia if you are on a budget or go and get some astia.
Lighting wise, light it like a copy stand, 45 degrees on each side, either polarize both the light sources or use a filter on your lens.



