Can't help you with the slides, but I have photographed many pieces of art for local artists, and various people who just have old photo's in old original frames.
I do it with my 20D/30D, a 580EX, light sphere PJ for diffusion, tripod, off shoe cord, and a circular polarizer.
The camera must be set on a tripod, I typically face it straight down and put the work on the ground. That way, everything is level. That is absolutely key, you can't have the work angled to the lens. A zoom lens is the best way to go, adjust focal length as needed to fit the dimensions of the frame. A circular polarizer should be added to the lens, this will help kill reflections from the glass. The diffused 580ex flash must then be attatched to the camera via the off shoe cord, and held out at a 45 degree angle to the piece of art. Then, fire!!!
Ideally, you need 2 flashes on either side of the piece being fired at 45 degrees so that the entire frame is lit evenly. If you use only one, you could get shadows on the edges, uneven distribution of light, ect. If your working with small pieces, then one flash will be fine, but for larger pieces, two is an absolute must. Otherwise, you will spend hhoouuurrrrsssss trying to get it right, and with 75 pieces to process, you don't want that!
I'm guessing you don't have this kind of cash to blow, but if I did, this is what I'd have:
Two 580EX's with ST-E2
Two cheap light stands
Two cheap umbrellas, softboxes, or LSPJ's. Not sure what would work best, only ever used the LSPJ
And a tripod with the arm thing
That's a lot of money though! I get by with 1 580ex hand held, but for 75 pieces..... eeeehhhhhhhhhh if they're paying you the $$, invest it.
Hope that helps some...