Anyone good with Windows?

So my brother emailed me in a panic, his friend's computer won't boot into Windows and he's scared to reinstall Windows in case he loses all her data. I know in theory reinstalling the OS is supposed to leave files untouched, but I also know that doesn't work very well. Does anyone know the black magic to save the files from the pre-boot screen? We've got as far as the Microsoft support documentation and some basic Google searches, anyone have anything better than that?

His description of the problem:

I have an XP disc. I booted it from the disc and it let me enter a recovery console. I tried a check disc recovery thing but that didnt help. If I run the fix boot program will it wipe all of R___'s data? Can I reinstall windows without wiping the C Drive? Is it easy? Is there a way of getting the data before reinstalling windows

Any suggestions much appreciated!

ETA: further question pulled up from the comments:

One little question, how do I get to the dos prompt? When I boot from the XP disc, I can enter the recovery console, reinstall windows or exit everything it seems to me. My research suggested that the recovery console doesn't give you enough access rights (?) to copy files to an external drive.