The problem with this is graceful degradation: if Javascript is off, as Masem indicates, you could have a problem with only half of it updating. If you're willing to require Javascript, you can do both updates through it using <a href="javascript:foo()"> where foo() is a function to handle the page updates for you.

If you're not willing to require JS, and you want to change multiple frames simultaneously, then reloading the whole frameset is probably the easiest way to go. You don't have to create a separate (temp?) file for each frame, just have them pass different params to the same CGI.

It depends on your target audience which of those you want to do--also depends, I suppose, on how many other frames you're not updating at the same time.