wow it's been a while since i heard about that card. i'm thinking a 4670 would do a decent job in its place. its not expensive, it's alot smaller than an 8800GTS and uses so little power that it doesn't need a separate connector.
If temperature is your main concern, i also have the same card in the same case and if you install rivatuner, free programme, and turn the fan speed to 75%, as stock is about 25% you will find your GPU temp will drop to about 48 degrees idle. It is a large card but running all games at 1680 x 1050 it handles anything on high settings including Crysis. I average 35 - 48 fps in Crysis so temps can be easily overcome if its your main concern. If you can fix your probs without spending money its always a bonus.
I would recommend the HD 4670 as mentioned before, but you may want to consider the HD 4830, or if you can wait a little while longer the HD 4770 will be coming out this month.
The HD 4770 should be selling for $99 and it's performance will be between the HD 4670 and 4830. Rumor has it that the HD 4830 will be phased out of production. The HD 4770 is designed to not need any additional 6-pin power connector.
The HD 4770 is expected to draw near the max power that can be delivered by the PCI-e X16 port, so overclocking will be limited in my opinion.
The 4670 would be a good replacement. In games that don't really need more than the 320MB of RAM that 8800GTS would be a little faster, but in more memory demanding games the 4670 should hold it's own. A better option for you though would probably be an nVidia 9600GT as it's faster than both that 8800GTS and the 4670, and while it seems a little bigger than the 4670 it's still smaller than that 8800GTS, and with a decent dual slot cooler it will run cooler. One complaint about the 4670 is that the stock cooler runs a little hot so since that's a concern for you then check out some reviews of 4670s that don't use the stock cooler and check the temps .