i am a Win 2003 Server admin too,
i don´t have the time to discover linux at this time. With two kids i have to manage my time very serious.
So i read a lot about Wimp, wamp and Lamp. Now we have wimp running php as isapi and the performance is good on a one year old dual Xeon Intelserver (Board, SATA-RAID5 controller .... all from Intel). One problem was the cpu-usage (60 %) at a very high Chatload. So changing to 10 sec. chat reload has solved this behavior.
Its easier to buy a better hardware than to try something complete new.
I have a presentation in german for how to configure php 5 and mysql 4 on a w2K3 server for sharing here (a lot of screenshots included).