If you installed the latest version of php for win32 (4.04) you DO have the imap extension. You just need to set your extension_dir prop in the php.ini file.
For example:
If you installed php in c:\php then it created c:\php\extensions. In your php.ini file find "extension_dir=" and set it:
extension_dir=c:\php\extensions
(or whatever your php install directory is).
Then uncomment out the imap line.
G'luck,
Jack