Weird Loss of Connectivity Issue -- Help?

Hi,

I'm on a cable connection, running through a Linksys Cable Gateway.

I cannot connect to the Internet via web browser, but can connect in every
other way (ping, Usenet, E-mail, etc....).

But here's the rub: I use a Cisco VPN client to connect to my office
servers. When the VPN client is installed on my machine (no vpn connection
initiated, just the client installed) I can usually browse normally. If I
lose my browsing ability, initiating a VPN connection restores it, and
keeps it restored for some time AFTER I drop the VPN connection.

If I uninstall the Cisco VPN client, I lose all browser connectivity (but
all other connectivity remains fine).

It's not a DNS problem, because I can't reach sites via straight IP.
Indeed, I can't even connect to my Linksys Gateway via browser.

Any ideas would be appreciated.

Thanks,
Kyle