Question...did you use StyleXP, some other program, or do it by hand?

If you used StyleXP or another program similar, there should have been a backup made of your boot ini and your ntoskrnl should still be intact.

Like Und3ertak3r said, use an XP cd to get into the repair console. Look for a backup copy of the boot.ini and restore it. StyleXP names it boot.bkk. If you did it by hand, I couldn't tell you what to do there.