Many suggested in this thread for that sort of money click here - look towards the end of the thread especially. Even better if you don't need a monitor. Btw, best single graphics card at the moment is an ATi HD4870X2, & a quad-core CPU will do well for now & the future.
Strange problem about not being able to load certain websites even after formats, etc. I guess you did try temporarily turning off security programs, different browsers & connecting directly - i.e. without the wireless? What about with SP3? I wouldn't be surprised it had something to do with Virgin! G