I have installed both Professional and Server and there are big differences versus the horsepower needed.

Professional can be a "pig" with less than 128Mb, and Server's sweet spot is 256Mb of memory. I tried both of them at the low end of 64/128 respectively and quickly upgraded the memory.

Both take much longer to install than NT. Server will actually sit, with no visual activity for long periods of time, and you will think something is wrong. Just don't get in a hurry, walk off and check on it every once in a while.

I'm assuming that the differences in Professional's and Server's IIS are similar for NT4 and that is that IIS on Workstation only allows 10 consecutive connections, you can't log activity, and you can't use virtual sites.