Stuck at loading screen, safemode doesn't work

I'm pretty sure I had a trojan or something cause my computer kept getting worse. I tried several scanning programs but none of them cleared it up completely.

Anyway, now I can't even get past the windows loading screen, and if I try to log in through safemode, I get stuck at the screen that says "SyS.multidisk....." or something.

Is there any way that I can log in dos mode or something and completely wipe my system clean and reinstall windows xp? I don't have the disk, it came with windows XP already on it. I don't care if I lose all my files, I just want a working computer again, free of any trojans or anything.

So, can I somehow log in dos mode or something (I don't even know how to do that), wipe everything clean, including whatever virus screwed up my comp, and reinstall windows XP without the disk? I'm assuming I have a copy of windows XP saved on my hard drive or something, cause my computer came with windows XP already installed and they didn't give me a disk.

OR is there some other way I can get in to clear up this problem?

Thanks so much for the help, I hope I can get my computer working again

 

Someone recommended
http://www.ultimatebootcd.com/
Is this a good alternative? I don't really know anything about it.