CiviCRM Community Forums (archive)

I have set CiviCRM 2.0 up for an organisation I support.  They are a UK charity and therefore encourage all their supporters to give via direct debit and to claim tax back.  So the basic situation is that we have three groups: Supporters (1), Direct Debit givers (2) and Tax-efficient givers (3).  I want to create a search that returns all contacts in group 1 who aren't in group 3 so we can write a letter saying: "Thankyou for giving, here's how to give more efficiently".  Or a search that returns all contacts in 1 who are not also in 2.
I've had a look at the custom search docs and will be trying it today but wondered if anyone had written something similar for 2.0 that I could base my custom search off?