Gaim is a multiple IM service client, like Trillian. It however seems to be pretty good. Half the memory footprint, and free + open source. I'll post a review in about a month when the honeymoon wears off.

There is a known problem when using Gaim with Cygwin (a linux environment for windows) if you have your system path set to the Cygwin bin dirs. The documentation for gaim actually hints at the fix:

If you have a Cygwin installation (with tcl 8.4), and have added its bin directory to your PATH, then WinGaim will crash on startup. The solution is to remove cygwin's bin directory from your path. Introducing Cygwin dlls into the native win32 environment is a very bad idea, and is likely to cause problems with other programs.

The fix is simple, instead of having the Cygwin paths on your global environment table, you just want it for your shell windows. Write up a simple little batch script to modify the path like so:

@echo off
set path=%PATH%;[Cygwin]\bin;[Cygwin]\usr\bin
echo This is my shell of DOOOOOOOOOOOOOM!

After that, setup a shortcut to: %windir%\system32\cmd.exe /K [your batch file]. The /K switch tells cmd to keep the shell window open. Bam. Cygwin and GAIM goodness.

Update: Sometimes Gaim will half-crash on startup. It won't actually die, but it won't do anything else either. This can happen if you install something like WinAVR which uses CygWin, and it adds itself to your path. If you find Gaim crashing all of the sudden, then check out each entry in your PATH environment variable and make sure there are no cygwin dlls.