Page menu: highlight a parent as current, even when on a subpage

Hello, I'm looking for some help with highlighting the current page in the page menu.

My website (here) has the following structure:

Home
Services
Portfolio
Non-fiction books
––––Series Title 1
––––––––Title 1
––––––––Title 2
––––––––Title 3
––––Series Title 2
––––––––Title 1
––––––––Title 2
Educational books
––––Series Title 1
––––––––Title 1
––––––––Title 2
About
Imprint


(Pages in Bold are excluded from the menu bar)

The pages 'Non fiction books' and 'Educational books', with their subpages, are actually part of the portfolio section, and although 'non fiction' and 'educational' are on the same heirarchal level as 'Portfolio', I have excluded them from the page menu. However, I would like the 'portfolio' button to remain highlighted when I am on these other pages and subpages. Until ATA 3.4.9 was released I was using page IDs and classes to do this, but having problems getting it to work in all versions of Internet Explorer (I'm far from being any kind of code writing expert btw). ATA 3.4.9 had a new css insert which overcame the Internet Explorer issues, however it doesn't use page IDs, or at least not in a way I recognise.

Attached is the code I used to create my main navigation before I replaced it with the ATA 3.4.9 solution. It's an unordered list contained in a table so a touch clunky and undynamic, I know, but it largely worked until it encountered Internet Explorer.

Also attached is the code from ATA 3.4.9 with some mods to suit my design and an addition to achieve the current page highlighting.

My question(s):

What should I do to the former, clunky table-based system to make it work in Internet Explorer (v7+)? or should I persist with the better, more dynamic and streamlined ATA code, and find a way to get the subpages showing as current.

Many thanks
Anthony

BTW I know about the rounded corners in IE and am accepting that limitation.