Windows Vista will be the last version of Windows for Pentium 4 and Core Duo owners. Microsoft has used its annual hardware engineering conference to announce that Windows Vista and Server 2008 will be the last versions of Windows to run on 32 bit computing.

According to APC Magazine

After the software giant has gotten over its hangover from partying like it's 1999 with the release of Windows Server 2008, it will have one last 32-bit hurrah with a "release 2" update to Windows Server 2008, and that'll be it.

32 bit CPU: if you have one, learn to love Vista -- you're stuck with it.32 bit CPU: if you have one, learn to love Vista -- you're stuck with it.There will be no more versions of Windows -- on desktop or server -- that will work on 32-bit CPUs like Pentium 4 or Core Duo (first-gen MacBook owners, take note, Windows Vista will be the last version of Windows installable on your machine.)

You can use Ubuntu Linux on 32 bit computer. It supports office apps, browsing, IM, email etc.