Even when on vacation, you find computers everywhere. Someone asked me, "what do I do? when I try to start my computer, I get a boot drive not found".
"Microsoft":http://support.microsoft.com/kb/321626 has a good discussion about what happens if you get Operating System Not Found or Missing operating system. The long and short of it is that you use Windows XP Recovery Console and then the fixmbr to update the master boot record if that is the problem.
There is also a good (finally!) discussion about all the "startup":http://support.microsoft.com/kb/308041/ problems you can have.
This has got to be the scariest message ever created. What it means normally is that (best case), the boot all the way to your hard drive has failed. The later happens quite a bit with notebooks, but let's hope for the best. "Windowsnetworking.com":http://www.windowsnetworking.com/articles_tutorials/Building-Using-Windows-XP-Boot-Disk.html has the best explanation of what is going on. In short, it is normally that the startup files have been corrupted.
If you have a floppy drive (an ancient machine!), then you can create a boot disk