When you often use a laptop on different netwoks you can very easily change your ip and much more by use this command. You can save the line in a batch file and run the file when you switch between home and work.
set address name="Local Area Connection" static 10.0.5.99 255.255.255.0 10.0.5.1 1
The syntax is:
More info on http://www.microsoft.com/technet/treeview/default.asp?url=/technet/prodtechnol/winxppro/proddocs/netsh_int_ip.asp
It is only tested in Windows XP Pro but I guess i can be used on windows 2000 and XP Home.