The Ti-400 and 500 were the first generation out. They'll only accept the original airport card internally, not the extreme. In my Ti-400, range was absolutely positively abysmal. 20'-25'. No signal on the patio.
If you want great range, get a PMCIA card. I've used both the Cisco Aironet (drivers available for both OS 9 and X) and the Buffalo 11-g (native support in 10.2.6 and up, no support for OS 9) and they're both wonderful. Full signal with no loss of bandwidth on the patio where the internal card didn't even know there was a signal.
For other recommendations, namely other cards that use the Broadcom chip which offers native support in Panther, see the networking forum, where you'll find all the info on airport etc.