One of the problems with being an office worker is that you're restricted from using the software of your choice. In the office, we use Outlook. After hours, I'm devoted to using Gmail. The way it threads messages is something I've loved since I was in the initial beta round. Sadly, Outlook doesn't have a way to do this with a click of the button... But there is a way to do so!
To mimic Gmail threads we need a way for Outlook to group by subject, but ignore the FW: and RE:. Luckily, it has just such a feature. It s called Conversation, and it's an optional column just like date received and subject. In your Inbox, go to the pane that lists your emails. Right-click any of the field headings, like From, or Subject, and select Field Chooser. You ll get a list of additional fields that pertain to your emails. Click and drag Conversation to the other field headings. You ll notice it looks just like subject, but ignores FW: and RE:.
There you go!