1. Mark all the rule groups as disabled and wait one week. The "one week" time period is because a rule group can't be deleted until MOm has groomed out any live data. If you have a four-day retention period before grooming, you would wait 4 days.
2. Delete the rule groups(s).
3. Delete the computer group(s).
4. You can delete any scripts that were used as part of the management pack - but be careful! Verify that the scripts are not used by any other rules.

Microsoft did have a knowledge base article discussing several methods to uninstalled management packs, but it has been pulled. In case it comes back, the link is http://support.microsoft.com/kb/918278.

Perhaps the easiest way to keep a management pack from functioning is through disabling the computer groups it uses (if they are not used elsewhere) or disabling its rule groups. Making a management pack non-functional is less work and a less risky process than actually deleting it.