The same way you'd transfer them between two XP systems. Assuming you've generated .xls, .doc and .ppt files using something like Libre Office, just drag 'n' drop them onto a mounted USB stick, move the stick over to your XP system and copy them back to your Windows hard disk. Simples!
I'm assuming two separate systems (you don't say whether this is so or whether you have a single dual booted one)
If dual booting, boot Linux, mount the Windows disk/partition and copy over between the Windows and Linux /home partition, again with drag 'n' drop.
Hope that helps, if not, please be more explicit.