Thanks, SuperSparks! (Spyware Dr, I realize that like everything else in life, CPU are ranked and pigeonholed; this article is interesting to you; computer-illiterate me won't even understand it).
I' ll go with 4GB of memory, if I must (it would be quite a jump from the current 512MB!). As far as HD, my present 80GB is still mostly "free space" (When I copy a DVD, its contents are stored on HD only temporarily; after a copy is completed, the contents are automatically deleted).
It looks that Win 7 Home to Pro is possible, although many things are quite nebulous for me http://store.microsoft.com/microsoft/Windows-Anytime-Upgrade-Windows-7-Home-Premium-to-Professional/product/C562285E