, This Memory
, This Processor
People will complain that this motherboard is no-name and the memory is "cheap", but our friend here is short on cash. Plus, several reviews prove that these pieces of hardware will be very reliable. And all of it (including integrated video) for under $150, plus a PCI-E slot if you want to upgrade. This combo is a steal, I highly recommend you get it.
Use your current hard drives, case, and power supply. Use the same IDE cable for your hard drives and optical drives. If your hard drives are SATA, then great, because this motherboard has the required connectors.
It should run XP fast, and Vista Basic decently. I recommend you stick with XP though, (haha).
As long as you don't overclock it, it won't be obsolete for another year or two.