run Automator
File->New
choose Application
scroll down and select Run AppleScript
right click in the area and paste the source code into the box
File->Export
Export As: pyrootOpener.app
Where: Applications
Save
go in Finder and find some ROOT file, right click and do Open With->Other
select pyrootOpener.app and check "Always Open With" box
you should get a prompt saying "pyrootOpener wants to do something or another with iTerm", say yes
it should work -- your file should open in PyROOT in a new iTerm tab and then pop up a TBrowser
it should do this every time you double-click a ROOT file in Finder