You didn't overclock your system. did you? i got that error when i overclocked to values that Linux was happy with, but MS just wouldn't take. Actually i got all sorts of weird and wonderful error after overclocking (which is why i don't anymore).
After reinstalling windows, odds are you need to reinstall linux as well, since WinXP will reclaim the MBR (which means, odds are you are screwed) So backup. A slackware install cd will allow you to manually mount your /dev/hdWhatever to say /mnt and /floppy meaning you can transfer data to a second hard drive (not second partiton, that'd defeat the purpose)
As for Windows saying a partition is inactive ... last time that happened to me, i had to kill the partition tables, and start from scratch. (hence the backup comment above)
Now having been the messenger of Doom, anyone wanna break g3nk1 some good news?
Alright, let me, this is why XP sux.