There are a number of good suggestions here. In terms of whether to use film or digital, and what formats and cameras, I'd start by making sure I understood your project well enough to give you good advice--am I right in understanding that you'd like to reproduce the artworks at their original size (e.g., 4'x6'?), not smaller reproductions of larger works?
If you do end up using a DSLR, I would suggest using a longer lens in general. Although your works are larger, I find that longer working distances (if you have the space) make it easier for me to line up the camera with the center of the artwork, and typically I end up with less geometric distortion, in the artwork photography I do, I end up using 100mm lengths quite a bit. But... only if you've got room.
If you end up photographing instead flatbed scanning, lighting is critical. The lights need create an even illumination over the entire artwork, which is harder with bigger pieces. Test your light setup, perhaps on a blank canvas.
There's a good pointer to some lighting tools in marcmccalmont's post, but there's one thing I'd do a lot differently than he suggests:
In addition to diffusers, I'd use a polarizing gel/filter in front of each light (e.g. http://www.adorama.com/LTP12.html
) and a circular polarizer at the camera. The polarizing gels can be juryrigged in front of the light or you can get filter stands.
Once you've got this working, turn the polarizing filter on the camera and watch the reflections appear and disappear off the painting depending on how far the filter is turned.
This lighting technique (in an otherwise dark studio, on flat art) can reduce pretty much every trace of stray reflections off of even the glossiest paintings, and that has a dramatic effect on colorful paintings in particular. Even on matte materials (say, pastel drawings on paper) the effect on the color can be huge. (Note: This technique, and many other techniques, do have troubles with metallic paints.)
One more thing: The lights need to be at about a 45 degree angle (maybe a bit less) to the surface of the painting.
Best of luck!