Borked that one, eh?
Never mind, fairly easy to fix. Just pop the XP CD in again and boot with it again. This time, instead of
installing XP, choose
repair. It should list both installs. Choose the original one on the 40G. Then choose fixboot. This should rewrite the boot files and allow you to boot the original OS.
Now, you can format the 8G drive from within XP, by choosing Manage from the right click drop down menu from My Computer on the desktop. When the Management Console opens, choose the disk management option from the left hand menu. You can format the smaller drive from in there. Reformat it to wipe out the extra XP install
Hope it fixes easy.
Cheers
Mick