"Cache" Logon settings: need help!


First post... I'm not a total "noob" but maybe one step above when it comes to Macs. I'm a 2000/2003 MCSE and I work for a Consultant in Spokane, WA. I recently setup a network which has 15+ Macs OSX 10.4 and one Windows 2003 SBS Server. I managed to get the macs to authenticate and logon through the active directory plugin in 10.4. Pretty sweet deal and pretty much works flawlessly. However, most of the macs are ibooks and are taken off site from time to time which in turns makes logging in using the network login username/password impossible! This is a major problem and I was wondering what options there are around it so that login can be used without being physically plugged into the network? In windows, it automatically cache's the login info and will allow a user to use his or her profile no matter where it is plugged in. Is there such an option on a Mac? thanks for your time and hope someone has an answer..