i've also got 2 old bigtowers...
AT... one is already modded for atx and thats my server now..
the other one was originally an old server case.. so it has the width of an atx.. and the hight of an AT-bigtower..
veerry modable!!

hope all my fans will fit in.
make sure u dont use those plastic mobo fasteners.. THEY SUCK!!!
one day i moved my server and *KLOUNK* the mobo fell down in the case... luckily for me everything still worked fine.. I could even move the mouse