Gfx Card Compatibility Help!

Hi Guys
i need to upgrade my pc with a better gfx card
but i need to find out if its compatible with my motherboard ect.
i have a
Packard Bell Imedia 1402
Intel Celeron D 2800mhz processor 3000 and summin max overclock
not sure as to the PSU as there is no sticker on the side
Motherboard is a Gigabyte GA-G8SIML
My current Graphics Card Is A Radeon 9250 (gay eh?)
My Motherboard supports Agp 4x
if more info is needed ask please

im looking atm at getting a Ati Hd Radeon 3450 but if i can i want to get a ATi radeon 3850 if possible

is there any website tht i can do compatibility test ive looked every on google and i cant find anything

any help much appreciated

Spohr