Step 1: Head down to Wally World (aka Wal-Mart). Check out the 6x9 boxes they have that are super cheap. You might just want to buy four of those and put your own speakers and mounts on there. The carpet lasts suprisingly well and it is easy to throw a mount on there. If you need some cheap ones just let me know, I have some for my speakers:
http://www.wakeworld.com/MB/Discus/messages/8/202516.html?1103578328 If you don't like Wally's boxes you can buy your own but have a good idea how to build them from what you saw there. And Wally has some really cheap truck bed liner stuff that works as good as all the rest(Plasti-cote in the Red can). Just build you a nice box then apply the Plasti-cote directly to the wood, it will take several coats and will leave a rough surface but it is shiny black and looks good on a tower. I hope the info helps. Good Luck and Post some pics for us...