Sounds like a DNS issue. I'm assuming you're office LAN connection is provided by a different company than your dialup service is? If so, sounds like a global DNS issue. To test this out, dial into your provider, and for the web address, type in (just this number, no HTTP or whatever) 66.218.71.81 . If that works, try typing
. If THAT fails, it's a DNS issue.
On your start menu, go to Start, Connect To, and Show All Connections. Right-click on your dialup connection, and go to Properties. Click the networking tab, select Internet Protocol TCP/IP, and hit properties. Make sure that obtain an IP address and obtain a DNS address automatically are selected.
I'm kind of confused as to why anyone would be in that connection changing a DNS address anyway. That's very rare that anyone would want to change that to anything other than obtain automatically.