Latest server binaries and source (version 1.52):

• x86 Win32 .DLL: as-1.52-x86-win32.zip
• x86 Linux .so: as-1.52-x86-linux.tar.gz
• Source code: as-1.52.tar.gz

A very useful resource for AQ2 server-related things is Wedge's website at http://action.wedge.net.

If you want a x86/SPARC Solaris binary, try http://www.planetquake.com/eclipse.