In Windows XP, go into the Network Connections then bring up the Properties of your network connection, then the Properties of the Internet (TCP/IP) configuration.
This is probably where you're accustomed to changing the IP address of this Network connection.
There's another tab: "Alternate Configuration". This will let you set up your shop address and configuration and the computer should switch between the two when you move it.
I don't personally use this; instead I have a separate PCMCIA network adapter I connect to the shop network. I also use that adapter for analysis tools with no IP address or protocols bound to it, so that's a reasonable approach for me.
[adder] Excellent hint, STL !