Officially, tethering is not supported on the original Droid. This means Verizon doesn't even offer a plan at an extra cost. It is available as an extra cost on the DroidX and Droid 2.
Unofficially, there are several apps that allow you to tether the original Droid. But keep in mind that it's against Verizon's TOS (terms of service). IF they catch you, they can charge you on a megabyte basis. That could be a very hefty bill. But current consensus is that Verizon cannot tell if you're browsing pages through your phones browser or your computer, so you should be safe. I've seen people here downloading tons of stuff on their computer using tethering and using up lots of bandwidth and they have no problems.
Feel free to tether, I do. But I just wanted to point out that's it's against your TOS. I used to use PDAnet which allows you to tether using your USB cable or bluetooth. Bluetooth is convenient as you don't need to carry a cable around, but it's not as reliable or fast as using a USB cable. I recently rooted my phone and now use my phone as a wifi hotspot (no cable needed anymore and very fast, but at the cost of using up serious battery juice).