How to get steam id:self.GUID=="Steam id")
(Copy & Past from : This thread)There is a clan tag function but it doesn't work for the PC since you don't use clan tags...
You can find a players SteamID on steamidfinder.com
Or, just use the code form the thread here: Call of Duty Modern Warfare 2 Server / GSC Modding - MPGH - MultiPlayer Game Hacking (Almost last)
OR, you can use the console and type in status and a long number (with chars) will be the Guid.