Windows 7 - Windows 7 on Apple Macbook--which version?

Which version would you recommend--32bit or 64bit--for installation on a Macbook (about 2 years old) with 4 Gig max of RAM?

If you don't know which one you need, x86.
It's also very difficult to recommend as we don't know your system specs, how/if you'd benefit from x64 architecture, if you can even run it...etc.
See #9 here.

I don't know if you can run a windows program on your Mac OS but if so this could help you decide.Fabe Windows 7 Upgrade Advisor - Download - Microsoft Windows

Here are the specs:

Macbook with 2.1 GHz Intel Core 2 Duo
4GB RAM
120GB had drive
Intel GMA X3100 graphics processor with 144MB of shared DDR2 SDRAM
Built-in iSight camera
Built-in AirPort Extreme Wi-Fi
Built-in Bluetooth 2.0
One FireWire 400 port
Two USB 2.0 ports
Built-in Gigabit Ethernet

I don't know whether the advisor will run unless I install some version of Windows first.

It's important that I know ahead of time whether to get 32bit or 64bit.

Thanks for your help.