Dont forget to backup the following:
Favorites,
Contact lists from outlook
documents,
pictures,
etc...

To do this simply pop in a floppy and move the files from your HDD to your floppy drive. The trick is finding where these files are in your HDD.
So to find favorites
C:\Documents and Settings\YOURUSERNAME\Favorites

To get outlook contacts:
Try this site:
http://www.outlook-express-backup.com/

Documents,
Simply go to your documents folder and drag and drop the files you want to save into your floppy. Make sure to check the size, floppy disks can only store 1.44Mb of data. So you might need to go get a 10-30 pack, depending on how much data you have.

Pictures,
Same as documents. Just watch the file size.

If you had a CDR or CDRW drive you could back it all up on one disk, using a burning program like easy cd creator or NERO. Much faster and easier.
Hope that helps,
and good luck with returning your defective PC.
BB
Before sending it back MAKE SURE TO FORMAT THE DRIVE USING THE DESTRUCTIVE RESTORE. That should get rid of any personal information and protect your privacy.