Reinstalling XP on a netbook, No MS CD/DVD

I have a Asus EEE Netbook (basic specs, 1.6 Atom processor, 1 gig RAM, etc). Over the last two years, despite defragging, uninstalling programs, virus protection, etc, it has slowed down to the point that it's getting quite frustrating. I love my netbook's size, weight, and, most importantly, would prefer not to have to buy a new machine at least until I graduate next summer.

Normally at this point I'd do what I always do with machines after a couple years: wipe the hard drive and install a fresh copy of Windows XP. Except this netbook has no CD/DVD drive, and I have no CD/DVD copy of Windows. I know I own a legit copy of the software. I know the code for the copy. My challenge is how to reinstall the software.

Does anyone know if there's a way to create a boot USB thumb drive from my running copy of Windows? Or perhaps I can prove to Microsoft I own a legit copy and get a CD or download or something for a nominal fee? I don't want to put money into this machine, but still does what I need it to do, basically.

Thanks very much
-Fred