ultrasawblade's answer will work (if your company has a VPN), but do you really want to drag all your local traffic (Sourcesafe and MSSQL etc.) through your Android phone (3G connection?). Ouch.
What you need to do is configure your two internet interfaces (wired(?) connection to LAN, USB-tethered WAN connection) to use different IP ranges and routes.
You don't mention what kind of system you're using (Windows?), so it's hard to give specific instructions, but basically you need to remove the default gateway from the interface which is connected to the LAN, and then configure the routing table to route LAN traffic away from your phone and through the correct interface. Here is a good article about windows routing tables.