Windows Weird Windows "Slow-Mo" prob

My brothers computer is messed up.

Its:

Jetway 867AS Mobo (KT266 DDR + SDR)
512MB PC133
1400 T-Bird
GeForceFX 5200
17.8Gig WD HDD
52x CDROM
550W Q-TEC PSU

I re-installed windows XP and it ran at like 1/8 of the speed its supposed to, and i dont just mean taking ages to load, everything ran in like slow motion.

Anyway, I decided to try windows me and the same thing happens. for example when I ran the me setup, it estimated 161 minutes to complete, I installed it earlier on my comp and it was 32 mins. Ive installed and now have the same problems.

Ive tried formatting and checking the HDD for erros, which is fine. Ive tried different IDE cable and messing with the settings in the BIOS> Nothing makes a difference. I dont have a clue what the prob is here. Anyone got any ideas ?