You have a few choices on this.
One way to do it is that you could just edit the template and add a link next to the thread with all the necessary information in the url to open a new window with the thread.
Another way is to get the showpost.php script from my
Markup Hack mod to make an easier link, that looks like this:
showpost.php?Number=74350
Or, you could install the entire Markup Hack package to get the extra [post] ubbcode/markup to link to a post like this:
74350
