Given the brief question, I don't know if this is exactly what you want to do, but you can run 32-bit ISAPI extensions (such as PHP, Rewrite, custom extensions, etc) in an AppPool in IIS 7 and 7.5.
For the full rundown, see this article here, the important part being:
...go into your IIS 7 manager console,
find the application pool your app is
running in, right-click on it, go to
Advanced Settings, and change the
Enable 32-bit Applications setting to
true... Now restart IIS (either via
the snap-in or the command line w/net
stop w3svc & net start w3svc) and
you’re good to go