Unfortunately.. no.... SLI isn't as flexible as crossfire when using different cards.... you need two identical cards for SLI.
Thx for the reply
But the 9800GT has the exact same chipset and board arrangement as the 8800GT (some oem simply rebranded the 8800GT to 9800GT)
I thought this can be an special case? Do you know if that's the case same as every other nvidia card?
Actually you can unlike what the noobs have said. Both cards are basically the same and use the same core even the 55nm 9800gt can still be used in sli with a older 65nm 8800/9800gt. The reason is because the core didn't change at all like the 5770 vs the 6770. The only difference is the bios. All you have to do is flash the 8800gt with a 9800gt bios but the clocks have to be very close to what they were before.
All he has to do is check the bios rom to make sure the clocks are in the limits of the 8800gt and the only thing that can complicate things is the timings on the vram but that usually doesn't pose to much of a problem. I can even mod the bios of a 9800gt to where it can be used in sli with either a 9800gtx or a gts250 by changing a few things without even touching the clocks, timings, or even what is enabled or disabled. The advantage to all these cards is that the core is all the same on all models except for what is enabled or disabled. The rest is all dictated by the driver and that is a different topic altogether.
Fermi era cards are different and pre geforce 8 era things can be changed but there are limitations. Fermi cards are more locked down and restricted than what people in my day enjoyed.