As I mentioned before, I have little experience first-hand with Vista. I do talk with users and read about other's experiences, however.
The best thing to do is to visit the suspect software's web site and see what the people creating the software say about Vista compatibility. Unfortunately, many companies see a new operating system as a chance to generate revenue; only their latest and greatest software is Vista compatible; the same goes for hardware manufacturers. This is not something new, we saw it with Windows 95, XP and now Vista.
Microsoft said several years ago that it could no longer maintain backward-compatibility with older software and hardware. Software companies and hardware makers want to push the limits and give the best they can and to do so they must support Vista, but only in the latest/new releases. Some hardware companies may create Vista-drivers for older equipment, but getting the full capabilities and Microsoft certification may be difficult. As Bill said, it depends on the hardware/software and how deeply it was tied into the XP/2000/Win## internals.
Keep us posted on what you find is, and is not, compatible.
D