AppleScript and Growl: How to choose the display style?
Each Applescript you use Growl with registers itself as a different application with Growl.

After the first time you use a script, you can go to Growl's settings. Look for the application name you registered the script as. (This is configurable in the register as application "Application Name" line when scripting Growl.)

Once you've used the script once, it should show up in Growl's settings. In there you can customize the display location and style specifically for that script, or as Growl calls it, that "application".

If you need more info about using Growl with Applescript, I have a blog post here, which explains how it works and provides a pre-built Applescript handler that you can drop into your scripts and call with a single line of code.