Hello,
(ANS) No.1 You have hit the nail on the head, sadly "the" major problem that does still exist is one of software compatibility. This means that with windows Vista. NOT all software is Vista compatible, especially older software.
No.2 Frankly this is something that makes me furious with both Microsoft and the software industry. Microsoft write a new version of windows only to find that many programs no longer work with it smoothly. YES! Microsoft's own software works nicely with there new OS but many third party programs don't funny that isn't it??
No.3 Further if Microsoft were not in such a frantic rush to push the next version of windows out of the Microsoft factory front door. Then many more software houses would have more of a chance to write new programs that ended up working with the new version of windows. But everyone is in such a frantic hurry and this results in poor programs that are still full of glitches because it wasn't tested correctly or the software is just not viable with something like Vista. Device drivers have been a dreadful problem with Vista too, many drivers didn't work with Vista and only 12mths after Vista's launch have some companies finally caught up with vista drivers for some devices.
No.4 SEE:- WikiPedia's Vista software compatibility listing which might be helpful in this context. Sorry! I don't have the URL in this machine but a quick Google or Yahoo search should finding it for you.
No.5 NOP!! if you have literally upgraded from XP to Vista i.e. installed vista over XP then the answer sadly is NO! you cannot now revert back to XP without wiping Vista and re-installing XP.
No.6 Some of your past XP software may still run in Vistas compatibility mode. You can run individual programs in compatibility mode and it ask's you which OS your programs ran under such as win98, NT, Win2k, XP SP2,etc.
No.7 Duel boot machines running XP or Vista can be set up but its NOT a simple task nor is it a straight forwards process either. Its not a novice task (no disrespect intended), its technically complicated more so than in the past because of the way MS have changed the way Vista boots in contrast to how XP boots.
kind regards Ivan
computer veteran, windows user since 1989.