Er...no!
The only operating system you've got is the pre-installed version of XP on the hard drive. You can't copy that to anywhere so, if you format the drive you'll have no operating system which will effectively render the PC useless.
Without an operating system on disk, you can't really move forward. (You can, of course, continue to use the existing installation of XP but if, or more likely 'when', something goes wrong, you won't be able to do anything about it).
If you definitely need to run Windows software, then you'll have to get hold of a Windows XP Home. (The Pro version has nothing extra to offer the average personal user). The only cheaper alternatives will be to get hold of an earlier version of Windows (which might be fine if you don't need to run the latest Windows software) or to install Linux from one of the cover-mount DVD's which have recently been issued by several magazines. (You can download these but, even on broadband, they're really massive downloads).
Chris