Need advice on upgrading from 32 bit to 64 bit

My PC configs are
RAM- 4GB
OS- Windows 7 32 bit
Harddisk- 500gb
inbuilt graphics- ati radeon 3200
external graphics- ati radeon 3870

My computer shows usable RAM of only 2.2 gb even though i have 4 gb RAM. One of my friends told me that it is due to my OS being 32 bit. I wont mind upgrading to 64 bit but i heard many programs dont work on it. Will there be an improve ment in my usable RAM if i upgrade? And is 64bit better for gaming?

If your system supports 64bit then I'd recommend it. It handles memory more efficiently. Your video card may be reserving RAM which would account for some of the 1.8 that you don't see.

As far as programs are concerned I have not been inconvenienced at all by any program and most manufacturers have 64bit versions.

I would check with your graphics card manufacturer to confirm that a 64bit version is available.