Upgrading an old computer (HP a350n)

Hey guys,

My lil'bro has this old comp:

http://h20000.www2.hp.com/bizsuppo [...] =c00041542

And I wanted to know if there was any way to get it to run SC2/D3/some future games semi-decently...

with a ram upgrade and a gpu upgrade along the lines of:

XFX Radeon HD 4650 600MHZ 1GB 800MHZ DDR2 AGP8X Dual DVI-I HDCP TV Out Video Card
or
EVGA E-GEFORCE 6200LE AGP 512MB DDR2 VGA DVI-I TV Out Video Card
or
Sapphire Radeon HD 3850 512MB GDDR3 AGP 2XDVI HDCP HDTV Out Video Card

This comp is not really my bro's...it's also my parents. And I was wondering if there was a way I could convince them to swap out the mobo and processor while keeping the case...don't know if that would be more cost effective in the long run. Anyway, this is the cheapest option, my questions are:

a) Will it work decently?

b) Is the cost worth it (around 200-250$ cdn as opposed to buying everything new for 600$)