Nils Luxton has written up a guide you can follow to get the latest (non-production) release of PHP - v5.4.0alpha1 - up and running on your machine in your WampServer instance.

I wanted to do exactly that, and at work we use WampServer so we can easily switch between PHP versions (and it also makes enabling/disabling extensions and options very easy – if you develop on Windows, check it out). Assuming you have WampServer installed, it is fairly trivial to manually install new versions of the AMP trifecta.

There's a few things you'll need to download to get things up and running (besides the new PHP version) but the rest of the guide is simple configuration and startup. If all goes well, you should be running the alpha in less than ten minutes.