How can I tell AutoHotKey to ignore the key (space bar) the executes the script?

":*:aaim::

Replace the first bit with that. It'll now fire when you type aaim, and nothing else. (That might be a little annoying if you're typing something that begins with aaim, but it's smart enough to not do it in the middle of words)"

"There is actually a function in AutoHotkey specifically for this purpose. ""Omit"" Note the O in the hotstring below:

:O:aaim::==aaim etc... etc...

For more information, open the AutoHotkey help file and click on ""Hotstrings & auto-replace"" in the contents menu. Omit is listed under the Options headline."