You have to install a recovery image first. I couldn't get my Droid to just install the update.zip. Droit Root Helper does a good job to help.
I used this tutorial to get 2.1 on my phone. However, the method they give did not give me su access. To get that I used this page:
SirPsychoS Recovery Image - Droid-Devs
SirPsychoS recovery image is the best for Droid IMO
To get ADB working, download the Android SDK for Mac (you need an Intel Mac for this) and extract the contents of the archive. Put it in your user folder, for example the path to mine is /Users/jeffnucci/androidsdk
There is a way you can add ADB to your .bash_profile but it never worked for me. So I always point the Terminal to the android sdk everytime I need to use ADB.
So open a new Terminal window and type this:
export PATH=${PATH}:/Users/YOUR-LOGIN-USERNAME/Documents/android-sdk-mac/tools
Make sure also that when using ADB your DROID is mounted and USB debugging is enabled. PM me if you need more help, or Gchat (in my sig) is quicker since I am at work a lot.
Hope that helps