Is there any benefit from installing Windows 7 64-bit when you have less than 4GB of RAM?

The other answers here cover the pros and cons fairly well, but consider this: if you think you'll be upgrading your memory in a year anyhow, and will be upgrading it to 4GB or more, then you might as well install Windows 7 x64 now, so that you don't have to reinstall later. It is not possible to do an in-place upgrade from a 32-bit installation to a 64-bit installation, so you may want to save yourself the trouble and just install the 64-bit version now.

I see only three potential benefits:

• 64-bit applications can grant you a performance boost, when higher numerical precision is needed. If you are only using your PC for stuff like Firefox or iTunes, you probably won't get a boost but if you are using some scientific or higher-demanding applications, it is definitely the way to go.

• Drivers are usually more stable since Microsoft requires 64-bit drivers to be certificated which does mean that at least some stress testing was done. 32-bit Windows do not have that requirement so manufacturers tend to be cheap. Unfortunately this also means that new drivers are usually first available for 32-bit version and 64-bit version may come little bit later.

• If you are developer, it may be useful for testing your application in 64-bit environment. When you have 64-bit Windows, you can test both 32-bit and 64-bit behavior.

Personally, I would stick with 32-bit Windows in this particular case unless you have very good reason.

Another benefit to using 64bit windows is that there are some other architecture changes that go along with the move from 32 to 64 bits - more registers for example. The 64bit operating system will be able to take advantage of those changes.