What software and hardware tools do you have available?
Microsoft Producer is a free program that will convert a powerpoint to an AVI file. You could try that to see if its any better looking.
Screen capture software is also avaialble for both PC and mac. You might try a free evaluation download but it will likely be save-disabled or watermarked in some way until you pay for it. But it would give you a sense of the quality level you get.
Scan-converting the output of the computer is another way to turn it into video. Scan converters come in versions less than a hundred bucks and over six grand. My opinion, having access to both ends of that spectrum, is that for casual use, all the under a grand ones are more or less the same quality, and you get what you pay for, starting over two grand and up, in terms of superior quality, ability to scale, remove flicker, things like that. If you live in a big town you might be able to rent a really good scan converter for a low one day cost.
When you export the stills from powerpoint, try .PNG and whatever other formats it offers besides JPG. (Though bitmap is probably going to always be hopeless.) Then when you bring these into photoshop, be sure you are not re-saving them as jpegs again, change the file format once you import to work with them, and save them as something better, I usually prefer targa files (.TGA) just because I’m accustomed to them and they work natively in my system, but also they are high quality and include alpha channels. Uprezzing in photoshop will be better than just about anywhere else you can do it. Also be doubly sure you are using the best method to import the shots into FCP. Look over the easy setups and custom setups so you can bring in native photoshop files or at least targas or the like, and not jpegs. Is your editing timeline working in Dv or something more high-resolution? That could have a great influence on graphics quality too.
Here’s a little trick that’s helped me work faster on things like this: if the powerpoint show has consistent backgrounds all the way thru, create or save out a photoshop file of a blank background with no text on it. Then you can use Apple Motion or stack it in the regular FCP timeline tracks and use simple masks to reveal your bullet points with keyframe accuracy without rebuilding the whole series of slides.
In the non-Mac NLE I use most, I have Inscriber Cg and what I can do to create quick, invisible “cheater” masks is use the eyedropper color tool to sample the frame and create a solid box layer in the CG the exact same colors, that I can interactivly manipulate in real time to reveal or cover parts of each frame, as many times as I need it, no rendering. I dunno if you can do the same trick in Motion or Livetype, might be worth exploring.
If you can, get the original powerpoint files and the program itself, and do your font and etc. tweaks there first, obviously. Then save and work in the highest rez all along the way. Good luck, let us know how it comes out.