Another update:

I tried to recover my HDDs using Knoppix 3.4 & 3.7 no success, Ubuntu 7.04 also.

Then I tried to install a rescue-winxp on an IDE HDD ... no success (maybe all my old IDEs are really out of order, dunno)

Now, what worked:
- reseted all BIOS settings to their fail-safe defaults
- disabled hyper threading
- removed all RAMs, inserted a new one
- disabled my on-chip SATA , enabled on-board SATA
- low-level-format of a SATA HDD which seemed to have errors last time -> now worked
- installed a rescue-xp on this SATA drive

Well, currently I'm copying about 150GiB date to my wife's pc ... looks good.

After that I will low-level format all my SATAs and reinstall everything ... WinXP and openSUSE

... this will take a while^^