XP startup loop and no access

I'm getting a little desperate, please help.
I have an old P3 Lifetec system with a fairly new Maxtor diamondmax 80GB harddisk. The disk is divided in four partitions, all containing at least some relevant data. I guess the system has been stable for too long! I know I should have followed a sensible back up stategy but haven't done so for too long.

Last week I was a little hasty perhaps in forcing the system to stop. After the restart it ended up in a startup loop after showing the black screen with the Windows logo and the little bar below it showing activity.
Starting in safe mode it shows that it runs (I think it is running or maybe installing) a long list of .sys files and stops at BTHidMgr.sys. It waits a while and restarts. I have renamed the this specific file but then it simply stops at the mup.sys that was one position before. So I suppose whatever should happen after HidMgr is where the show stops.

Telling it (via F8) to not restart, it stops at a BSOD with the error code STOP: 0x0000007B(0xF8B15528, 0xc0000034,0x00000000,0x00000000).

I can see the disk correctly (as far I I can judge) in BIOS. With UBCD4WIN I can see the drive in system manager, but not in disk manager and neither in My Computer. With the XP setup CD it does not access the disk in Recovery console nor in setup. So I cannot access the partitions from this windows environment.

Starting the PC with an old windows 98 start-up diskette I do get access to the partitions on a DOS level, with truncated names such as 'docume~1' for 'documents and settings'.

I have an old 5G harddisk added as a slave, which I can also access at DOS level. So what I could do is draw the total tree of the C partition on paper down to the deepest file level and copy collections of say 4.5G to the slave. Then start up UBCD4WIN and move these files to my external USB harddrive (which is not found at DOS level) and repeat this until I have most of the C drive copied, hoping that I can later filter out the relevant data assuming the long Windows filenames come back.

After this immensely mindkilling exercise I could try to format C at Dos level and hope that Windows Set Up wil do its job and start collecting all drivers and programs I had installed and finally try to get the datafiles associated with these programmes back to their right position from the USB drive. Sounds like a weeks work!

With Google I find more or less similar problems all over the net, bu no solutions that work for me so far.

Hope someone can help me to solve ( and preferably understand) this....