Thanks for letting me know about the mysql error, I'm still brushing up the code on that
To have the pages contain all the components of your shopping cart, the categories, etc., don't edit cart.php to use home_main.tpl and instead keep it using home.tpl
With that however you wont get the tabs, etc. across the top. You could take the tab code and integrate it into your home.tpl if you wished.
If it's not working correctly, then likely there was an error made in your installation. If you PM me ftp details I'll have a look for you.