Whichever way you choose to have the navigation tabs, I'd have the chosen tab / page highlighted in someway so the user knows where they are.
Move the legal stuff from the bottom left to the bottom right, it's too close to the navigation menu.
The colorized titles are nice, but they're pushing the content down into the page and it's getting close to the 'fold' of the screen.
Stick a couple of points onto your line height. Ideally, 14pt, it makes for more readable type. if you have deep paragraphs, people are far less inclined to read it.
Don't put your email addresses into your pages. This is inviting trouble. If your email is so easy to access, the spammers will find it.
I sincerely hope you're going to have secure socket layer on the payment page?
Just a few thoughts, take it or leave it .. it's up to you...