Go to Start>Run. Type it "boot.ini" and click ok. If it does not find it, that means (obviously) that your boot.ini file was somehow deleted/renamed.
You have two routes you can take. Please try the first one first, because it is the easier of the two, and, if performed correctly, nothing but the Windows folder will be touched.
1) Pop in your Windows disk, and do a Windows repair. You can google it if you don't know how to do that.
2) This one is a bit more complicated, and may possibly be hazardous (to Windows/your HDD). If you choose this option, i am telling you that you need to make a system restore point.
That way, if anything goes wrong after this, you can restore back to the point before doing anything.
You can open Notepad (Start>Run>All Programs>Accessories>Notepad.exe) and copy this into it:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Edition" /fastdetect
Save it as "boot.ini" and then open up "My Computer" (Start>My Computer). Double-click your C:\ drive and move the "boot.ini" file there.