Comcast migraton causes some LAN users to lose IE and Outlook connection.

This morning our business migrated from TIme Warner to Comcast. Now two of my LAN users are unable to access IE or Email (via Outlook or outlook express). However, they ARE able to access ICQ, and anything INTERNAL is accessible as well. Any ideas on what could be the problem? I can’t get Comcast to call me back. Out of an entire office, these are the only two that have the problem.
Could it be the version of IE that they are using? If so, that would be strange, because the rest of us are using the same version. ANY assistance is greatly appreciated!