When you installed a second copy of Windows on the same partiton, do you mean you performed a repair install or a complete installation (is that possible? I don't recall the option form the XP setup program)
A repair installation sounds like it would work.
You can also try using a "live cd" to boot the computer and access the hard drive without having to load Windows. I have done this before and it is very, very handy (did I mention it was handy?) I prefer the Ultimate Boot CD for Windows
. Read the instructions thoroughly. You'll need a blank CD-R or CD-RW, your Windows XP service pack 2 cd (there is a way to do it if your CD is not SP2, check the website) and a working computer with an internet connecion and a CD burner. After you copy your files to a disk, you can perform a complete reinstall of Windows. The UBCD4Win also has many tools for repairing you existing installation, you may want to explore those options after you've backed up your data.