Can't Download From POP Account When Logged Into Domain

Any suggestions would be appreciated...I am unable to download email from my POP account when I am logged into my domain (I can send email fine). When I am off of the domain (i.e. at home) downloading works fine. My stats are...Dell Latitude D620 Clean Install of Vista with all updates current Office 2003 (Outlook 2003) with all updates current The POP account is the only email account set up (we are not using exchange)SBS 2003 is my Domain controller with all updates current. I did have to download a patch from MS to get the Vista machine registered on my domain. This is the only machine running Vista the other 4 on my domain are XP and obviously working fine.I currently do not have any antivirus software installed on the Vista machine but I am running MS Defender (which came preinstalled from Dell)I tried turning MS Defender and the Firewall off but that did not have any effect.Repeated reboots had no effectI am guessing that there has be something (a policy perhaps) that is interacting between my domain controller and Vista machine but I did not see anything in the policies relating to this.One other fact that may or may not be related, the first message in the queue had an Excel workbook attachment (about 214Kb in size)When I set up Outlook to download from another POP account (Yahoo), it downloaded the messages from that account first then they both hung up once it got to the messages on my original account. The messages from Yahoo never got marked as downloaded. Because when I hit send and receive again, the Yahoo messages downloaded again. This happened 3 times (same messages came down three times) before I took the Yahoo POP account of the send/receive group.