I tried a simple google at http://www.google.com/search?&q=lenovo+t400+drivers and the second hit lists the modem driver at http://www-307.ibm.com/pc/support/site.wss/MIGR-72858.html
Be sure to install drivers in the order XP DEMANDS.
Windows XP has been loaded on my T400. When i launhed the Lenovo System Toolbox, it says that i sould reinstall the driver of these two components 'PCI Simple Communications Controller' and 'Modem Device on High Definition Audio Bus'. When i launched the System Update, it doesnt show any required driver or update to load. And, i look for these drivers on Lenovo Website but i couldnt find anything.
How can i fix my problem? Thanks.........