While it's possible to move a folder or drive to Favorites in the Finder Sidebar there's no obvious way to put your Computer in the Favorites section.
I like to have my Computer at the top of the Sidebar. Here's how using Terminal and TextEdit.
Convert ~/Library/Preferences/com.apple.sidebarlists.plist to XML and open it:
plutil -convert xml1 ~/Library/Preferences/com.apple.sidebarlists.plist
open -a TextEdit ~/Library/Preferences/com.apple.sidebarlists.plist
Find Computer. It should look something like this:
<string>Computer</string>
<key>SpecialID</string>
<integer>8399481092</integer>
<key>Visibility</string>
<string>NeverVisible</string>
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110801143846226