Which Windows 7 to install?

"The Windows 7 system requirements declares 2GB as minimum for 64-bit.
Going by earlier system requirement statements from Microsoft, I would suggest using 32-bit.

If you are attracted to 64-bit (I do not see a reason for that in recent times)
You could upgrade your memory and start with the 64-bit edition.

Other references.

Gizmodo: Why You Should Go 64-Bit With Windows 7

If you're not planning on going to 4GB of RAM anytime soon, you might wanna hold back, since you need 4GB of RAM to take full advantage of 64-bit's memory management. That said, RAM is so disgustingly cheap right now, and has such an intense bang-to-buck ratio, you should definitely upgrade to 4GB if you haven't already. Anyone who runs specialized or older gear should probably not jump into 64-bit.
Windows7 Forums: Windows 7: 64 bit vs 32 bit? -- 64 bit pro and cons
You can address much more than 4GB of memory [whole idea is, handle more memory]
16 bit applications will no longer run
Existing 32 bit drivers no longer work
Unsigned kernel-mode drivers no longer work
Running some 32 bit applications on a 64 bit OS could actually be slower
The Microsoft 32-bit and 64-bit Windows FAQ
linked from Windows 7 features, 64-bit support page"

"For any PC with less than 3GB of RAM I would go for 32-bit Windows. If you plan on upgrading your RAM and you are sure you can get 64-bit drivers for all your hardware, go with 64-bit Windows. You probably won't find many Windows 7 drivers yet, but 64-bit Vista drivers should do fine.

32-bit software usually runs fine on 64-bit Windows 7 (and Vista). Since I started using Vista 64-bit (around the time it got released), I've only experienced problems two times and only one was a complete failure. An average user should not have any problems using 32-bit software when 64-bit is not available."

"It used to be that 32-bit was recommended unless you specifically needed 64.

I think these days the reverse goes. Unless you have hardware that does not have supported 64-bit drivers, or you have applications that are absolutely not going to work on 64, I'd say pick 64-bit.

It is only a matter of time before you put more memory into the machine. Also, since 64-bit has a larger addressable memory space (even if there is no physical memory available to cover it), some applications will actually work better because they can provide apps with more virtual memory."

"If you planning extend RAM to 4GB+, it's better if you install 64bit version.

Or if you want virtualizing 64bit OS in virtual machine."

"64 bit handles ram more effectively than 32 bit (i.e. u need to have more than 4gb)

Word of caution though before you install make sure that you can locate 64bit drivers (for your laptop) and 64 bit compatible software (depends on what software you use) especially if you are going to be running 3D applications.

If all the above parameters are certain then I'd say go with the 64 bit version

Edit: Atleast in terms of 64bit Windows Vista i have seen a marked difference in performance of 3D applications (3D Max and Maya) when compared to the 32 bit version (the configuration of the computers the OS was installed on being the same)"