Request timed out..when pinging a

The Situation: I have a client who has a dedicated port to the Internet. They have Proxy 2.0 and IIS 4.0 in place for the Interent Access. I am switching them from an Exchange-based (internal) e-mail system to a hosted POP3/SMTP-Outlook solution.
The Problem: I can ping from the workstation by where it finds the IP address of the servers, but the request times out. I have DNS and default gateway settings at the workstations, and ICMP in place. (I am using Windows 2000 at the client PCs.) I am thinking it has something to do with the IPSec in place, however, in review, there are very little restrictions.

Any suggestions would be GREATLY appreciated!

-Kath