Need to do a very quick custom theme

I have a couple of hours to convert my website to WordPress (I’m new to WP). I figured I’d simply make a copy of Twenty Ten, rename it and use WordPress’ editor to inject my CSS and XHTML… needless to say after opening up header.php I was at a lost of what to do (its been a long all nighter plus my web design skills are rusty). Mainly I’m afraid of ripping out the wrong WP code and spending more time fixing those mistakes. Its a simple one column site throughout (no widgets), its a web store so I’m essentially using this as a CMS (no blog, comments, archive, etc.) and the only plugin I’m using is WP e-Commerce so any of the Twenty Ten theme’s (or a recommended theme that’s easier) guts that makes plugins work properly need to stay in tact.

Any kind of help would be greatly appreciated!