SBS2003- Roaming profiles

The network has a SBS2003 Premium server with 2 NIC’s. The clients are using XP Pro. I want the users to be able to go to any PC and be able to check their mail. At present they have to be in the local admin group for this to work. The rest of their roaming profile works fine.

Ideally I do not want the users to be in the local admin group. Is there another way to get this to work?