|1. refurbed boards are generally ok, as long as the original damage/fail was minimal, eg, blown/faulty capacitor, dry solder joint etc. if it has been affected by a lightning strike or power surge, then chances are other components will begin to fail after it's ben refurbed. also, the savings from new to refurb are pretty marginal, i would always opt for new.|
2. again, you can pick up a low end dual core for much the same price as a P4, which means you'll have a decent tide-over
3. your motherboard would determine which type and size of memory you can use, as well as your OS.
Windows 7 x64
Intel® Core™2 Duo CPU E8500 @ 4.1GHz
ATI Radeon HD4870
8GB OCZ Platinum 1066
2x Samsung 1TB Spinpoint F1