My current system is a ACER ASPIRE M1641 (2GB ddr2, intel E2220, 320GB, built-in GeForce 7050, Vista home premium), very cheap and a shitty thing. I bought the 4850 to have some boost, but system couldn't stay stable for more than 3 weeks. This is why I'm upgrade mobo,ram and cpu.
The reason its not stable is the psu. If you do plan on getting those parts, do yourself a favor and get a more quality unit.