First off, you'd never want both of them walking independently it will cause tons of problems later on.

Have the shaman follow the warrior so you can control the warrior, and have the shaman heal, dps, whatever you want him to do.

A basic script would have one key set to your focus key, so whenever you press a spell it automatically makes the secondary target your target. It's also not a bad idea to have a follow button.

If you are not used to modifiers, your going to have to get used to it, or buy xkeys, and still worry about it.

It's not hard to learn how to script AHK, there is a thread on it if you give me a few minutes I will find it.

Here- http://www.dual-boxing.com/forums2/viewtopic.php?t=807