You might want to consider simply using paypals shopping cart, it would save alot of hassle integrating zen cart, and I have found that the paypal shopping cart is actually easier to integrate than just sending the total to paypal and receiving the confirmation code back and dealing with it.
On another note, I found the graphics/ page VERY slow to load. Have you optimised the images? They really only need to be 80% jpgs for the photos not 100% quality, as the extra 20% makes no real noticable difference on a computer screen (it's only needed for printing)
Have a look here for a speed report which might help in sorting out the lag on load time
(is the header PNG optimised for the web?)
I'm viewing the page with Firefox, and the menu is squashed to the left, which just seems wrong with all the rest of the page (main page) being centred, I'd consider centering everything just to make it look right, you could also put some cool background motifs down the far right and left hand side to give the site a more cohesive look (just watch file size, use a repeating low quality gif if possible) I'm thinking of something which is in keeping with the walking bear theme, and doesn't look tacky, (don't put it behind any of the text).
I really like the bear moving with the menu, it's very effective, and the site is certainly getting there, it's going to look great when you've finished!
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Sometimes, when my code just won't behave, I take it outside and make it listen to britney spears music, and when it comes back it's really well behaved. I wonder if it's suffering from post tramatic stress syndrome now..