Uncheck the use default gateway on host to get your LAN connectivity to still function... But before I give you the Google on this, let me state your post is too vague for me to tell you that this is the definitive fix. But it's the most likely one.
In parting, why didn't your IT staff support note this?
http://www.google.com/search?&q=uncheck+%22use+default+gateway+on+remote+network%22
We got this new software that requires the use of a modem. How do i install the modem with an existing LAN that provides the computer with its Internet. This software support people say the only way it will work is with a modem. How do i Set it up to look for the modem for its connections and everything else still use the IP address for the internet from the LAN. Im new so bear with me thanks. The LAN is apart of an Entire School Districts network.

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