It doesn't get any easier than the package at the link Naina gave above, almost too easy
That site seems to keep very up to date versions as well, the PHP version in that package is currently 5.2.6
Thought I might add that you can use ColdFusion with the WAMP package as well.
Macromedia allows you to download ColdFusion free of charge and use it in Developer mode which will restrict the number of remote hosts that can connect (2 I think), and you can use it indefinitely in Developer mode.
When installing CF it asks some easy to understand questions about how you want to use it, you tell it where your Apache configuration and web root are, and away you go, you can develop cfm on WAMP.
Be warned though that CF install will add a bunch of services running at startup on your development machine, I was hoping it would only run it's services when Apache started, but no such luck.
On the bright side, other than using an extra 130-140megs of RAM, I do not notice a hit on CPU cycles, so if you have plenty of RAM you should be fine, I have WinXP SP3 with 2gigs RAM on a P4 3.2Ghz single proc w/hyperthreading.