Whatever you root the phone with probably will come with the Wireless Tether app. If not, get it from Android Market.
Can you tether it to more than one computer/wireless device though?
This is what I was wondering last night. Are you just "tethering" the droid or is the droid actually becoming a 802.11b/g access point that multiple devices can connect to. I'm not interested in tethering just one laptop to the phone. My goal was to create a 100% real, 100% portable "access point"
The cradlepoint setup in the picture above is a real 802.11b/g AP. I can have up to 32 other laptops, cameras, ipods, , WIFI SD Cards, nintendo DS etc within 100 feet of me connect to the internet via my cradlepoint access point just like they would connect to a wireless router in their home.