Here are some useful documents for Extreme Networks Switches. Extreme Networks makes the highest performance network equipment currently available. Benchmarks against Cisco clearly show them washing down the floor, mopping it up, drying it nicely, then waxing and polishing it to mirror shine. 

Fortunately for LANparty's, the push of carriers to 10gig in the data centre has meant a flood of very high capacity gig switching routers into the second hand market place. Of particular interest are the Extreme Networks Summit 'i' series, with relatively low port numbers and huge switching capacity making ideal core switches for bandwidth hungry lan events. Similarly Black Diamond chassis make for excellent cores for larger lans with tiered of fully collapsed networks.

The Consolidated Hardware Guide gives excellent detail for Summit 20-24, 200-48, 1i, 5i, 48i, 48si and 7i series Switches, as well as Alpine 3800 and Black Diamond 6800 series.  This will give you some idea of what these switches can do before you cough up your hard earned cash for them.

With your switch in hand, the ExtremeWare Command Reference Guide will show you how to actually use your switch. No their isnt really a GUI... but if you need one then this kind of hardware isnt really for you.

There is a handy walkthrough on how to reset the switches password (if you dont know it... chances are you wont) here.