Centrino Wireless technology should work perfectly on Win2kPro however, it just depends if there are Windows 2000 compatible drivers available for your mothers laptop model & make.
I presume it came with Windows XP? if so leave it on, Windows XP / Pro is fine for anyone, especially your mother since she has a son with IT knowledge.
Just install a Firewall (Sygate Personal Firewall) - Disable System Restore, Disable Windows Messaging Service, Disable File & Print Sharing, Install AVG 7 or something similiar, Install Mozilla FireFox for web browsing (if you have to disguise the Icon as the IE 6 icon :)), Install Mozilla Thunderbird as a replacement for Outlook (if so disguise the icon as the Outlook\Express Icon), Install Spybot S&D and set it to run when she first boots up, and to auto update.
As for the wireless, she should be able to move between Wireless networks perfectly (secure / public one's) as long as someone enters the wireless WPA Encryption key as per which network she is connected, the computers software should remember this. - Just set the wireless to connect to what ever network it feels is better (the one with the strongest signal).