a few days ago, in the middle of a random link post, i mentioned i was using a registry hack to get my WM6 mobile to act as a Wifi router, which was allowing me to connect to the web though the iPod Touch when not at home. Well, thanks to the magic that is XDA-Developers, there is now a program, called WMWifiRouter, which does this automagically for you. It runs on Windows Mobile 6, and should work with 5 also.
The idea is quite simple: install and run the software, setup an AdHoc wireless network, and run the software. your device will connect to this network, and you should connect your wifi enabled device to this network too. and your sorted! More details on the site. the software is being updated fairly regular so new tweaks and features are being added all the time.