There's a command to "call out" a target (I believe it's shift+space but it's been a while) and a command to assist your target (I believe "t" -- it's been a while). Spacebar will automatically run you to that target and start autoattacking.

Inside your menu there's a list of keybindings. Unbind your 'wasd' keys, rebind the "call target" on everyone except your main, perhaps rebind your 1-8 keys on your alts, and you should be golden.

GW seems like an easily multibox-able game from what I remembered back when I played. That was pre-Nightfall. :P