Well, I've been playing around with XP64 for a couple of days now, & have some more info on compatability.
Hardware:
No real probs so far [aside from a bug in Setpoint 3.3 & 4, more on that in a moment].
Asrock AM2NF3-VSTA: no problems, but haven't tried the onboard sound. [edit: onboard sound works fine in XP64, Dilli should know, it used to be his board

]
Audigy 1: seems to work ok so far, though at first I had no sound; for some reason an option to mute all was both turned on & hard to find. Used the drivers from WU, as the Creative ones didn't want to install properly.
Radeon X800 GTO: works fine so far, the 1 let-down is that there's no 64bit version of Hydravision, which is seriously out of date & only [obviously] works on [some] 32bit progs.
Logitech MX1000: Works ok, now that I've found a non-buggy version of Setpoint to use with it. Although the 32bit v. of Setpoint 2.4 has the ability to change what the different buttons do, that function is missing in the 64bit version of 2.4. Setpoint 3.3 & 4 have a bug that somehow interferes with monitors being put into standby. With either of those versions installed, it doesn't matter whether the mouse is perfectly still, or even turned off, if you try to put your monitor[s] into standby [e.g. with a keyboard shortcut], it/they will immediately "wake up" again. [this bug is also in 32bit version of 4.0, but haven't tried 32bit 3.x on XP32]
Software that's made for 64bit:
7-Zip [totally 64bit]
SpeedFan 4.33: prog is still 32bit, but it has a 64bit driver to make it work with XP64.
TweakUI for XP64
UXTheme Multi-Patcher 5.5: Lets you use other Visual Styles in Windows [works for XP32 as well], without having to buy StyleXP. Why MS made the file in such a way that it would only work with the default 3 Styles is beyond me.
ALZip v7.0 beta 1 [Free registration required to get the beta version, otherwise you have to settle for v6.7, which I don't think has support for 64bit shell extension menus, though the main prog in v7 is still 32bit]
Media Player Classic Home Cinema [a spin-off of the main MPC project]
Vista Codec x64 Components: works on XP64 as well.
32bit software that works in XP64:
RocketDock
EditPad Lite
AveDesk 1.3
WinAmp 5.5: Works fine, but I'd advise everyone to go over the install options with the proverbial fine-toothed comb, as there's a bunch of stuff some people wouldn't want installed [e.g. Yahoo Toolbar].
EULAlyzer: Very useful for checking long EULAs to see what the company is trying to sneak past you.
Kaspersky Anti-Virus 7
Shutdown Tray
Orbit Downloader
DU Meter
DNSKong
Proxomitron: That site has a link for a patch which improves the interface [had to be patched by someone else, as the original programmer died]
MailWasher Pro 6
CCleaner
NetMeter: Freeware DU Meter clone.
DigiGuide
Restart: Very useful little prog if you dual/multi-boot between different versions of Windows [not Vista though].
NeoTrace Pro [old IP addy/web address tracing prog, not found anything newer that I like yet, but it still works.

& of course the 32bit versions of Firefox & Thunderbird.
Software that doesn't work in XP64:
PathCopy 4: An amazingly useful shell extension, that doesn't work on XP64.
That's it for now, more soon.
