The G33M02 is a Socket 775 board, and an 1155 CPU will not fit. I'd suggest an E5400 or better Pentium Dual Core CPU.
As for the videocard, I'd suggest something more modern like a Sapphire 6450 or better yet, 6570. The 6570 is said to be among the ultimate HTPC cards, and it's not that expensive.
4gb of DDR2 is a good idea, but there's no need to upgrade the power supply unless it's failing or too noisy.