Your color scheme is not very pleasing. The colors are all over the place. Consider using a two- or three-color scheme, using complementary colors. The tabs aren't bad, but the selected tab has black text on a dark background, and is unreadable. If you have to use a color other than white, then consider another light color. I'd recommend the "disabled" tag be a light color with black text, and the current tab be the dark color with white text.
Your View Cart link should be more prominent. It looks like you're trying to hide it in the corner.
In some pages, your content is right up against the border. White space around your borders is a good thing.
Try to get away from using tables for your layout. Go to the Zen Garden and learn how to use CSS to make flexible, pleasing layouts.
Study sites like Amazon.com to see what sort of things work, and what doesn't. Good start, though!