I've been stealthing the FTL macro posts and found them to be a little complicated, so I thought I'd share my own FTL-type setup.

I use HotkeyNet, which is a great app (and free). It's a bit complicated to get started with, but once you get the hang of it, it's an amazing tool for multiboxing. Anyway, my little guide assumes basic knowledge of HKN, so it's just the FTL-type part I'm writing:

I have my basic maillabels as such:

Code:
<Label pal Local SendWinM P1>
<Label shm1 Local SendWinM P2>
<Label shm2 Local SendWinM P3>
<Label shm3 Local SendWinM P4>
<Label shm4 Local SendWinM P5>
On top of that I have an "assist" template:

Code:
<Template Assist>
    <If ActiveWinIs P1>
        <Sendlabel shm1,shm2,shm3,shm4>
                <Key Ctrl Alt F6>    

    <Else If ActiveWinIs P2>
        <Sendlabel pal,shm2,shm3,shm4>
                <Key Ctrl Alt F7>    
         
    <Else If ActiveWinIs P3>
        <Sendlabel pal,shm1,shm3,shm4>
                <Key Ctrl Alt F8>    

    <Else If ActiveWinIs P4>
        <Sendlabel pal,shm1,shm2,shm4>
                <Key Ctrl Alt F9>    

    <Else If ActiveWinIs P5>
        <Sendlabel pal,shm1,shm2,shm3>
                <Key Ctrl Alt F10>            
    <EndIf>
<EndTemplate>
As you can see, it sends a different key to each client, depending on, which window is active.

On each toon I have keys mapped to assist the slaves (in this case Ctrl Alt F6-F10, but it could be anything). I use bindpad to make the assist macros, but you can use the default interface too, just keep in mind that it takes up 4-5 macro slots.

My ingame assist macro is as basic as it gets i.e.:

Code:
/assist Cottuy
Let's say the active window is P1 (my paladin). In this case it will send Ctrl Alt F6 to my four shaman, which is bound to my macro which does the following:

Code:
/assist <paladin>
Now, when I create a DPS button, I'll simply do the following:

Code:
<Hotkey Q>
    <ApplyTemplate Assist>
    <Sendlabel shm1,shm2,shm3,shm4>
        <Key %trigger%>
This will work with pretty much all multiboxable games that support assist. However, it presses two keys with the same keypress (i.e. Ctrl Alt F6 followed by Q), so to make it WoW-legal it has to be a roundrobin/toggle (which is odd since /click macros which also hits several buttons is perfectly legal):

Code:
<Hotkey Q>
    <Toggle>
        <ApplyTemplate Assist>
    <Toggle>
        <Sendlabel shm1,shm2,shm3,shm4>
            <Key %trigger%>
Another option is to have Ctrl Alt F6 in game mapped to a macro which does:

Code:
/assist <paladin>
/click <dpsbutton>
That would mean one macro for each type of spell/sequence, so that's not really desirable.

The great thing about this type of this setup is that if you for some reason need to play the char solo, you don't have to reconfigure at all, since the assist-macro is seperate from the casting macro, so there's no targetting being done in the casting macro at all.

You can, of course, apply the same principle to follow, target etc etc.