It won't overheat as long as you don't go crazy with your OC. The trick to overclocking is in knowing when to stop. Crank up the speed completely beyond the operating limits of the GPU, CPU, system bus, or RAM, and the PC will crash or freeze a lot. The best way to OC your video card is to use coobits.
NVidia has even built overclocking settings into its latest drivers. To enable them, open the Windows Registry editor by going to Start, Run, typing regedit, and pressing Enter. Go to "HKEY_LOCAL_MACHINE/SOFTWARE/NVIDIA Corporation/Global/NVTweak/," right-click the right pane of the editor and choose to add a new DWord called coolbits. Edit that entry and give it a hex value of 3, then close your Registry editor. The NVidia tab under your PC's advanced display properties settings will now feature a new "Clock Frequency Settings" page that allows you to adjust memory and graphics chip clock speeds for your board. Click the "Detect Optimal Frequencies" button if you want the utility to try to find safe overclocked settings for your graphics board. In my opinion, this doesn't always give you the best stable OC.
When I performed the optimal test on my card, it crashed it some games but works great in a general Windows environment doing regular things like Word Processing, playing AOEII, etc. So you may have to tweak it further by manually bumping down the clock rates.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?