I also wanted to know that will the ram change?
Because right now i have 2gb
i saw onlne after installing this it'll be 1780 mb (1.78gb)
If your OS is a 32bit system then you could go either one more gig or two gigs. The 32bit system will not recognize any more then 3.5 gigs. But if your OS is 64bit then you could get a lot more than 4gigs.
Your budget of $80.00 is not going to get you a new CPU and a GPU. It will get you the 6670. But a 4 core CPU is going to run about $70.00 and the other problem is will your MOBO allow the up grade.
You might have to up grade your MOBO to get a better CPU. Then there is the PSU will it be enough for all the up grades. So by the time you do all this up grading you might just want to build your self a PC.
But for now the HD 6670 is the way to go. It will work good on some games and others it won't because of your CPU. I do wish you good luck and I hope everythings works out for you.
the 4 core CPU from AMD = http://shop.amd.com/us/All/Detail/Processor/ADX631XWNZ43GX