Three notes to this:

The SP2 now available is a test set.

The installer works, so does the uninstaller. The installer archives your old files in system and system32 directories and many .dll files in Windows directory, backs up registry, and creates a restore point and makes an Add\remove programs entry in the Control Panel while installing-- to run the uninstaller, you scroll down to the Windows SP2 RC2 entry, click, and click remove. Install took between 30 and 40 minutes on my 3GHz Prescott box, and replaced between 2 and 3 thousand files. Uninstall took about 25 minutes, and worked fine. Allow lots of time for this install. I installed from the full English CAB\redistributable file.

XP is a bit slower and the Window behavior is altered after install of this set. Widnow behavior was visibly different, especially as to how you get responses from toggling the taskbar app running buttons, one click brought a window not in froeground to foreground, another click closed, app or CMD session window in foreground already closed normally.

Restart twice to get your speed back, the first restart will be slow, even on my 3 GHz box it took 4X normal for the first restart after install with lots of blank screening, and before restart even happened my taksbar hid and unhid 6 times durign first restart.

Windows will be a bit slower after install. Folding still works, both Gromacs cores and Tinker cores, console clients, and all programs I had work (I was up until after 2 AM this morning function testing major things).

What gets installed, partial list:

Memory managment got a big overhaul.

IE went to 6.0 SP2 and worked faster than before afterwards.

Full forced DirectX 9.0b+ install occurs (some folks are calling this 9.0c or d).

OLE32 got replaced, kernel got replaced, VMM functionality got partially replaced. This a very major rework of core Windows functionality.

The EULA with SP2 forbids installing this tech preview on a production box without a full backup being done first, in my case I did a full restore point set first, never used it as the uninstall rolled back right.