I would suggest for a $150 budget to go AMD.
Here is one CPU and mobo setup
a 3.1 Ghz Athlon II x3, that has a chance that you can unlock a 4th core. - $75http://www.newegg.com/Product/Product.aspx?Item=N82E16819103872
a MSI 785GTM-E45 AM3/AM2+/AM2 AMD 785G HDMI Micro ATX AMD Motherboard - $70http://www.newegg.com/Product/Product.aspx?Item=N82E16813130237
The GPU, and PSU should work. If that is really 184pin ram, then its DDR-1 which would HAVE to be replaced. There is no DDR-1 mobos anymore, plus that stuff is slow.
New DDR3-1333 (2x2GB) will cost you another $70. You really want to have DDR3 ram if you want to play Black Ops.