Sorry about your troubles. Did a quick search on PHP5 but could not find any Vista related issues, other than Apache server install problems.
You may want to browse this list to see if you have any additional apps that potentially may not work.
Windows Vista RTM Software Compatibility List - IeXwiki
Recently distributed Vista SP1 does NOT resolve many of these issues so I suggest sticking with XP for at least year.
I am looking to upgrade to Vista Biz 64-bit (so I can use 4gb of memory) and run Windows XP inside VMWare to use day-to-day apps.
Good luck!