Based on the following site:

http://www.adobe.com/products/flashplayer/systemreqs/

I need the following minimum spec to play 1080p flash video via a browser:

CPU: 1.8GHz Intel Core Duo, AMD Athlon 64 X2 4200+, or faster processor 
RAM: 512MB of RAM
GPU: 64MB of graphics memory

I only have a 2.8GHz Pentium 4 process which is no where near as good as the processor listed above. I don't want to upgrade my processor as I think it will mean I have to change the motherboard etc. So, my question is, what is the cheapest PCI-E GPU I can buy which will allow me to play smooth 1080p flash video via a browser. I think the cheapest I can get is the 8400GS, but am not sure if that will be able to handle 1080p with the processor I have. I have looked at the GT520 and was wondering if this is the cheapest GPU which I need, or if there is something cheaper which will do 1080p with a 2.8GHz Pentium 4. Or, will I have to get something better than a GT520?