My good computer (athlon 64x2) has a 9800 GTX+ GPU in it.
I have an older computer my 8 year old son uses to play online games (at low-med settings resolutions 1024x768 or 800x600) sometimes. It is an AcerPowerFG (apfg-u-5161) that has a pciex16 (not 2.0) slot in it. The CPU is a P4 (2.8GHz).
It has a liteon (Ps6301-08a) 300W power supply (no pcie power plugs I can see).
I put a pcie Radeon 9250 (256MB) GPU in it years ago.
The problem is the 9250 wont do pixel shader 2.0 and I have recently found some games it just wont work on, which makes my son feel left out. I am would like to find a cheap way to get a couple years more out of it and I am looking for options or recommendations you have.
If I could put the 8800 GTX+ in the old acer pciex16 slot I could buy myself a nicer GPU. Is that possible? To do so will I need to buy a new PSU with 2 pcie6 plugs? Any cheap PSU recommendations?
If not is there a really cheap pciex16 GPU that will not require a new PSU but will run newer games at low-medium settings as well as or better than the 9250?
You wont see the benefits of your old good card in his older machine as the CPU will restrict its performance somewhat.
By far your best bet is to buy a 4670 for his comp and if possable up the memory to 2gb as newer games even those a year or so old will benefit from it.
Resell your good PC's card on a well known auction site and you should make back a good chunk if not all that the 4670 will cost you.
All you have left to worry about then is upgrading your own PC.
PS a 8400 or 9400 would make good door stops or possibly frisbees
I'd say you shouldn't spend too much on your sons computer and just get him a cheap 9500GT. While a 4670 is faster it may not be a good bet if the PSU in that acer is of poor quality (which it likely is). Going with anything faster is a bit of a waste with that old P4 CPU in there. While giving him your 9800GTX+ would give you an excuse to put a faster card in your system, you will need to buy a decent PSU for your sons system and the 9800GTX+ would really be held back by his CPU so you wouldn't see much benefit in that system over a cheaper Radeon 4670.
If I decide to move the 9800 I am now thinking a good PSU like this 500W OCZ http://www.newegg.com/Product/Product.aspx?Item=N82E168...
which will be used as the PSU for the athlon 64x2 and the 750W PSU currently in the athlon will be used in my next computer (which will be when XP is not viable or the P4 motherboard dies). This way I would be spending nothing on my sons computer, just kind of buying parts for the next computer early. (Think my wife will buy that?)
In any case I have a couple weeks to ponder. How much GPU prices drop will probably be the deciding factor.