At the time of writing, version 1.61 is the latest version and has lots of nice new tricks up its sleeve. There are versions floating around the web you can use, you know what to do with the following:
After obtaining a .deb file, make sure you've installed OpenSSH in Cydia on your phone. Then, all that's left is to scp it up to your iphone:
scp pdanet1.33.deb email@example.com:/var/root
The password would be alpine or dottie, unless you've changed this manually. Then ssh into your phone with the same password:
And install the PdaNet package:
dpkg -i ./pdanet1.33.deb
Restart your iPhone and there you have it! Tethering over WiFi. If you managed to get version 1.61, then you can tether via the USB cable, but only if your computer is Mac or Windows (no Linux).