Hey. Took me awhile (and a false start with WAMP) to get XAMPP running under Server 2012 x64 but it looks real good now - and most of the time was prep, undoing many Micro$oft security features. Next time I'm sure it will be lots quicker. The XAMPP installation itself was actually a breeze, after the prep-learning-curve.
Thought I'd share with anyone who has issues with this.
Installed to the default c:\xampp folder. But first - disabled as many security features in S2012 that I could - turned off IE security, disabled UAC, logged in as "administrator" (not just an account that has admin privileges).
I had already installed the MS Visual C++ Libraries, so not sure if these were needed for XAMPP.
I left IIS running on the server, so I changed the HTTP and HTTPS ports for Apache to 85 and 4430 in httpd.conf and httpd-ssl.conf respectively. Didn't realize that these ports can be changed in the control panel, so I edited the aforementioned files.
I did not install Mercury, since this is to be in part an hmailserver machine; I did install FileZilla and Tomcat but have not checked these yet. (BTW, hmailserver seems to also be running fine. I still need to come back and get Squirrelmail working, but first things first - I need a break!).
Apache, PHP, and MySQL seem to be fine so far.
I've also enabled some of the security features as suggested in http://localhost/security/xamppsecurity.php (in my case ...localhost:85/security...)
To everyone involved in this project: Nice work, all!
I hope to come back here to comment further on my progress. Not yet in "production" - still testing.
8-23-2014: Added path to both php and perl in Windows environment (not sure how necessary this was), and registered the .php and .pl extensions with Windows.