Press Alt+G after selecting the text
;Google lookup
!g::
OldClipboard:= Clipboard
Clipboard:= ""
Send, ^c ;copies selected text
ClipWait
Run http://www.google.com/search?q=%Clipboard%
Sleep 200
Clipboard:= OldClipboard
Return
Edit: Part of the script had been converted to a link and was not showing properly. I've now edited this.