I have a HP Pavillion a1512x desktop running @ 2.80 mhz w/4gb memory the graphics is handled by an Intel (r)82945g Intel intergrated (r)82945g chipset family video card. I want to upgrade to a better monitor and this chipset will not handle it so I was wondering if I could upgrade to a ATI Radeon HD 4850 or possibly a XFX HD 577A-ZNDC Radeon 5770. I use this machine mostly for photographic work. I have an empty PCI Express x16 expansion slot.
those cards would be bottlenecked by your cpu and your powersupply would probably not handle those cards. i would take a look on an ati 4670 or 5670. those are low power cards and probably could run on your system.
if you don't game and all you want to do is photoshop, an ATI 5450 or 4550 will do the trick.