You also have "Windows 7 Firewall Control" – link : http://www.sphinx-soft.com/ -
It's available in different versions (free – plus – portable), very light resources wise, and user friendly interface. Very easy to setup.
Won't exactly help on XP?
Back to OP here - with 512MiB of RAM, do not overload your system. Use limited user account (do not work as administrator), sandbox for browsing. MBAM+SAS free on-demand only. Maybe Priwatefirewall, give it a try. L'n'S I am using is paid, no free version.
If you want help with the SuRun + SRP part, I can post some details. Shouldn't be complicated provided that you do things properly immediately after formatting your drive and reinstalling Windows,
before you have installed anything else.