goto htc.com and download htc sync it gets the drivers all set up for you

HTC Mobile Phone Support - DROID ERIS by HTC (Verizon) - Downloads

 

if its saying adb not found you need to make sure your in the right directory. also if your using a mac make sure you put ./adb and not just adb

 

Because they are referring to C:\sdk\tools, I am guessing that they are not on a Mac.

Open My Computer, then open C:\ See if you see the sdk folder there. It could be name something different, and you will need to know the full directory name.

Example: C:\android-sdk-windows\tools

Once you find the folder then you can open the command prompt, and type:
1) cd C:\android-sdk-windows\tools <or whatever your path is>
2) dir <this will show you a list of files, if you don't see adb.exe, you are in the wrong folder>