Vista 32 bit = XP 32 bit + extra bloat (plus a few nice spangly additions) anyone that says it is less compatible for ANY reason other than the odd Aero problem (which can be disabled as and when needed) really hasnt tried Vista 32 bit... Yes I know they say Vista was a "totally new core" but thats just not true and we all know it, no self respecting company would take a perfectly servicable basic framework and chuck it away. I can guarantee the basic Vista sub system is a tweaked and updatd version of what you find in XP.
Now Vista 64 bit is built around XP 64 bit, and like XP 64 bit there are still driver issues and its likely that as long as HW companies think 32 bit and 3.5GB RAM limits is the future (and some still do...) then there is likely to be a few issues with some HW or software that utilises system level drivers.
I personally have had 32 bit Vista Business since the day it was released and have so far not been able to install one 5 year old game because its MSI install package was hardcoded to only accept upto windows xp (it wouldnt work under x64 when i had that either..) Nothing a quick MSI edit couldnt fix.
Even non supported HW (of which i now have nothing, but my computer is reasonably new throughut) would work using previous XP drivers if it was really necessery!
Seriousely. We use windows because it looks nice and allows us to run any software we want to buy, Vista is just like XP was to 2000 or 98, more of the same, tweaked, with added bloated bits but just enough extra polish to make it feel worthwhile.
I use Vista and XP daily, one on my main machine one on my laptop. I hate going back to XP as it all just feels that little bit less slick, that little bit more clunky. I know its all down to animations in the GUI and tricks of the eye such as hw rendered transparancy, but I dont care, thats why I bought a kick ass PC!!