If anyone googles how to do this, here is the solution we found, it works with unsaved windows (hence the "untitled", you would have to change that depending on your use)
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In the command, execute the system comand (ours is Ruby, so backticks)
`osascript switch_windows.applescript`
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Then in your Support directory, the file: switch_windows.applescript
tell application "TextMate"
activate
end tell
tell application "System Events"
set found_window to false
set all_windows to every window of process "TextMate"
repeat with w in all_windows
if name of w contains "untitled" then
set editor_window to name of w
set found_window to true
end if
end repeat
if found_window then
tell process "TextMate"
tell menu bar 1
tell menu bar item "Window"
tell menu "Window"
click menu item editor_window
end tell
end tell
end tell
end tell
end if
end tell