Follow these instructions to be able to run peerblock and still run Steam and get updates and such!
1) Open peerblock
2) Click List Manager
3) Click add
4) Put anything you want in the description, such as "Steam/Valve"
5) Check the "Add URL" radio button
6) Enter this url: http://list.iblocklist.com/?list=steam
7) Choose "Allow" under type
8) Hit OK!
Done! Now you can run peer block and still be able to run steam!