Do I need to download anything before I can play this?
Technically no. We have both a serverside (no client needed) and a client side (full mod options) server. The server side version allows you to join a game without the client. You will be unable to bind keys to set weapon options without the client, however.
Also, the SHIFTER vehicles are in the client side server only.
Client is light weight @ about 2.5mb - a ShifterClient.vl2 file is copied to your base folder and does not interfere with other mods or game play (base, classic, etc)
Client File: http://shiftermod.com/download/ShifterClientPack.exe
Once you've done this, you can go to SETTINGS> CONTROLS and look in your keyboard settings for any options that start with [ S ]
(i.e. [ S ] Weapon options).
Then you can take your plasma rifle for example, and select standard, twin fire or quad fire mode.. Command Detonated mortars are nice, and very handy against pesky scouts, too. EMP mortars are my fave.. No shields, oops!