I can't think of a way you could get the return code of the script that is executed remotely. I think what I would do is modify the script to also write the result somewhere. It could be a file, an entry in the event log or in the registry. You could either keep a running log or delete the entry/file so that you always have the latest result.
The way I might tackle this is run through the list of computers and spawn off the remote script. Wait for enough time for the remote script to finish on all the computers, then go through the list again, collect the results and send the email.
Jeffery Hicks
Microsoft PowerShell MVP
SAPIEN Technologies - Scripting, Simplified. www.SAPIEN.com
blog: http://blog.SAPIEN.com