Installation error: Could not load ntkrnlmp.exe - error 7

HELP
Been running XP on my main PC for couple of years now with no problems until few days ago when my modem stopped dialling out - moved it to this machine and works OK, ran spybot, adaware and AVG with no significant results and so decided that it would be a good idea to reinstall XP from the CD in case corrupted files were causing the problem. Halfway through installation it got stuck on "39 minutes remaining" and further tries got same results. Decided to try the XP boot floppies and got the message that " Could not load ntkrnlmp.exe - error 7 ".
As I can no longer access the original OS I can do nothing on that machine. Can anyone suggest a next logical step - If I could load MSDOS, I could at least access files.
I need to either get back to my original XP OS so I can try a different installation disc (We own 2 copies of XP PRO) or toi remove the old OS entirely so I can reinstall from another CD.

TIA