You'll first want to start with a custom inventory to collect that information. A custom inventory for a registry key isn't really all that hard. I'd suggest looking at the examples Altiris provides in their KB.
https://kb.altiris.com/article.asp?article=4237&p=1
Once you've got those downloaded, you'll want to edit the "RegkeyValue" files to fit the key you're looking to inventory.
I know you're supposed to roll that into your regular inventory, but I've taken to running these as separate software delivery tasks.
After you've collected this information you'll be able to create a Collection by either using a Filter to that newly created data class or by entering the SQL directly to get a list of those computers.
Hopefully that puts you on the right track