Since your processor is a 32bit CPU you can only run a 32bit system. The fact that it says amd64 or it calls the 32bit version intel does not matter. Ubuntu can support both architectures(AMD and Intel). Use the 32bit version. :)
However I would recommend getting 13.04 if your using it as a desktop environment. Many speed improvements have been implemented in this version.
If you want to check if your CPU is infact a 64bit CPU this is how to do so:
Open System by clicking the Start button, right-clicking Computer, and then clicking Properties.
Under System, you can view the system type.
If your computer is running Windows XP, do the following:
Right-click My Computer, and then click Properties.
If you don't see "x64 Edition" listed, then you're running the 32-bit version of Windows XP.
If "x64 Edition" is listed under System, you're running the 64-bit version of Windows XP.
Type this in the terminal
If the output contains this:
CPU op-mode(s): 32-bit, 64-bit
Rather than this:
CPU op-mode(s): 32-bit
You have a 64bit CPU