Hey man! I think I got a solution for you!
I was wondering how to create an executable .term file myself and found a breakthrough when I realized that Leopard implemented quite a few changes in Terminal.app -- namely, in the preferences window.
Here's what I did:
1. Open Terminal.app
2. Open preferences (Command + ,)
3. Notice how Terminal now has 4 tabs in Leopard! Click on the Settings tab and select a template on the left that you like (this will be the layout for your new .term file). Click the little wheel icon at the bottom and select "Duplicate Settings". This will now create a backup of the original template with which to work with (i.e. edit with an Execution String).
4. Give the new Duplicate a name of your choice. If you'd like, edit the window's size (i.e. columns, rows, the title, etc.) When your all done and ready, click the "Shell" button/tab on the right hand side (still in the overall "Settings" tab).
5. Check the little box next to "Run command" and enter your shell command in the right! This is the equivalent to the ExecutionString code on 10.4's .term file.
6. You can tweak it further by editing the "When the shell exits", or window size, etc. -- anything you like.
7. Once you've tweaked all your settings, click on the little wheel again and select "Export..." and save your .term file!
Now you can always double click on your new .term file and it'll launch your command just like before because you've tweaked its Execution String!!!
Hope this helps!
*Happy Holidays =)*