|To start with, this is the CPU/overclocking forum...you should be asking in the hardware forum.|
The HD4650 is a weak card & definitely can't take advantage of 1GB memory, plus it's slow GDDR2 memory instead of fast GDDR3. Choose another card.
And you realize you're looking at a 100% rebuild, right? New CPU, board, RAM, video card & power supply. The only things you can use from the old HP are the case (maybe) & the drives.