I had crashes a couple days ago in game with the 81.98 drivers after an couple hours.
however, I'm now using the new 84.12 drivers and the 1.0x version of the game, played for 6 hours last night, not one crash, this is with a 7800gt. So the latest beta drivers certainly work with the game, and the patch did help the temp issue...
You can grab them here;
ftp://download.nvidia.com/Windows/84.12
I doubt thats it though.
Since Civ 4 crashes, I bet your power supply is not so good, or you have a desperate need for more cooling, (temps in the mids 50's are fine for that card. 80 would be bad, 70 not so good), or your ram timings are to tight (if you've never messed with them that probably isnt it). But Im just a computer tech who builds a lot of AMD boxes with nvidias cards in them
Usually its the power supply. When you launch a game suddenly the cpu and graphics card draw maximum juice, in your case probably another ~60 watts of power, and your power supply cant handle it.
If you can post your power supply specs, maker and amps support on the +3.3, +5, and +12 volt rails. As well as how many drives you have I could let you know fairly certainly if thats it...
There should be a label on the side, that looks like this;
http://images10.newegg.com/NeweggImage/productimage/17-103-457-03.JPG
just read it and post the amps. I'll check back a couple times.
good luck
Oh, if it is the power supply. You can swap one out in 5 minutes on your own, all the connectors only key one way, and only fit the things they are suppose to connect to, you only need to remove 4 screws to take one out...
It is quite easy, as long as you dont forget to plug something back in, which is usually pretty obvious

This is not something you need a tech for. However a good supply for your system will run between $60 and $90, anything that selling for less then $40 is complete junk...