TechCrunch reported several days ago that Froyo will allow tethering, and even allow your phone to become a portable WiFi hotspot.
If you want tethering today, though, it's easily available, using PDAnet for Android software. It works for both Macs and PCs. You'll be able to tether using either a USB cable or Bluetooth. It's exceptionally easy to use. Install the software, connect your phone and computer via cable or Bluetooth and you're online.
The PDANet software on your Android device gives you connection information such as the amount of data you've transferred. When you connect via a USB cable, your Android phone charges as well. Here's a screenshot of PDAnet on an Android phone.
It doesn't work via WiFi and can't turn your phone into a WiFi hotspot, so Android 2.2 will be superior. Still, if you want tethering now, it's available.
Keep in mind that tethering may or may not be allowed by your data plan, so check first.