Hey
This sounds like what I have got going on here:
http://www.spectre256.com/php/bmdb/cp.php
If you click on the tab, the page is reloaded but the tab that was clicked is now 'active'.
How I did it (same for you) :
Duplicate the CSS class you have for the TRs - bodytitle6 I think yours is, not sure.
Make the necessary changes to the formatting to make it different from the other TRs so that it would appear 'active'.
Now is the tricky part of replacing your css class with an if statement. This if should look at your GET variable and determine if it is active or not. If it is, then the new 'active' class should ECHO and if not then the bodytitle6 class is ECHO'd.
I haven't had a proper look over your code but it sounds exactly like my tabbing system.