User Groups in Vista

I want to change the security settings on a file (my personal finances) so
that only my Admin account has access. However, by default the Users group
has read access. If I set that to DENY, then my Admin account cannot read
the fikle; apparently Admin users are part of the Users group, and the Deny
policy in Users group overrides the Read policy for Admins.

I'd like to remove Admin from the Users group, but I cannot find the way to
modify Groups.

I tried the trick on the Vista website about running MMC and adding the
'Local Users and Groups' snap-in, but Vista says that the snap-in cannot be
used with Vista.

Anyone have any suggestions?

Thanks,
Jason