This Christmas I plan on getting my sister a graphics card for her HP machine (1-2 year old, HP Pavillion Media Center, AMD 4200X2, 2GB RAM, nothing flashy...). She likes to play the Sims 2 and has high expectations for the Sims 3. Money is not a problem for me; however, given the fact that my sister's computer is your standard, run of the mill OEM rig, I'm not sure about the power supply, cooling, etc.
Currently, her machine has nVidia's on-board 6150 graphics card and I'm thinking that a HD 4550 or a 9500 GT would be a reasonable improvement and not threaten the stability of her computer. What do you all think? Can I go higher? Any ideas?
I'd look at the 4670. Should be about as fast as a 9600gso/8800gs, but is made to not have to use an external power connector. May want to check the specs of the card vs the psu, but I think that card should be fine, maybe a small memory upgrade as well.
I second the HD4670, mine's running things like Stalker, Prey, Bioshock, and Rainbow Six Vegas 2 at all high settings at 1440x900. No way it won't run Sims 3 maxed. And it runs perfectly nicely on a crap PSU.
First check the capability / connection of the mobo.
Even the GF9600GSO / HD4650/70 are overkill for her needs for both the type of game and resolution.
The HD4650 doesn't require much power or a power connector, and neither does the GF9500GT, nor the HD4550. All are capable for those needs and both can be found for under $50 (the 9500GT for under $40 even), and they can be found with quite reliable and passive cooling.
BTW, Since it's an OEM case you may also need to get a half-height or low profile card, and these solutions also have those options too, look for them if you find you need it (maybe check the HP's knowledgebase/forum and see what others did for that type of rig).