The only practical way we have discovered so far is changing the
stylesheets so that the classes that apply to links  can be forced into
opening in a new window.

This is admittedly a bit of a all or nothing approach, be interested to
see what others have done

If I understand you correctly you would like to change the manner in which clicked links  open in WSS. By default links added to a Team Site open up in the same browser window  as the Team Site causing some ugly navigation issues taking your customers away from your site.

This was one of those things I was very happy to figure out and afterwards felt stupid I didn't figure it out because it is an easy fix. Short answer is FrontPage2003.

Longer Answer:
1. Open up the desired team site in FrontPage 2003
2. Locate the web  part you'd like to change the links to open in new browser
3. Right click on the link
4. Select "Hyperlink Properties" from the menu
5. Select "Target Frame"
6. "New Window" > OK

Save this, refresh your browser and give it a look. Remember you will need administration access on the Team Site to see the "Hyperlink Properties" section.