Originally Posted by VGeorgie

It's a little more complicated than limiting to 3GB for 32 bit, but basically the max physical RAM is 4GB, but each virtual process sees 2GB, or 3GB with the IMAGE_FILE_LARGE_ADDRESS_AWARE set.

If I were you, and if this machine is going to be used for tasks other than rendering, I would NOT replace your 32-bit Win7. Instead, get a second full copy of 64-bit Win7 and install it in an extra partition. You can then boot your machine in 32-bit mode, where all your software will work. Or, when you need it boot into 64-bit for video editing. There are some blogs that lead through the steps to do this, or take your box back to the guys that put it together in the first place.

Programs that are 32-bit only run in the 32-bit space in Win7/64, but it's not always smooth. Legacy software can crash, or simply refuse to run. I have some older custom software like this.