I think I had this problem once with my other computer...
When you boot does a menu flash for about a second? Something about booting Windows or Windows (Original)? If so, next time you boot, move the arrow keys up and down b4 youy get to the screen, so that when it comes up, the auto-choose option doesn't automatically go to that "Continue Setup".
If not, try to see if booting safe mode allows you to enter taht menu. If you do, pick the Original (I think its that one) and you should be able to boot into Windows. ONce in there you can back up all yoru stuff, and even just fix that prob by checking your boot.ini.
Right-clik on My COmputer
Startup and Recovery Setttings
Default should be:
I tihnk what the XP install does is add some setup files to the first partition (hda1, or w/e you wanna call it, most ocmputers have 2 partitions premade) and XP is usually on hda2. The boot.ini is somehoew editted during this and when a messed up install happens, this boot.ini is left with the option to boot the first partition, which brings you to that continue setup screen.
Hopes this works