Wow, you get past the ntoskrnl.exe error? That's the 'kernel' itself, Jonny. The heart of Windows. No ntoskrnl, no operating system. Dalek may be onto something there.
Check any modification dates on that particular file. If you've got another XP machine handy, compare not only mod dates, but also file size against what's on the Toshiba. Bear in mind any difference in XP versions when comparing the ntoskrnl file on the two machines. Unfortunately, I'm not near an XP unit at this time, or I'd give you that info.
Yeah, learning is in the doing. I learned more working on my nephews' computers than on about any others. Jeez, it's appalling how far a little porn can go in screwing up a Windows PC. :(