I found this cool site that allows you to turn your css design into a wordpress theme. It's perfect for matching up the design for a newly installed wordpress blog on an existing site. It is really easy to use. You just create an account and get started. You need your stylesheet and the html to plug into a few forms. You do have to edit your html layout with some tokens so the content and sidebar of your new blog fall into the right places. The site is called themespress.com.
With ThemesPress, you can create your own WordPress theme in a four simple steps:
1. Upload the images your design uses
2. Copy the HTML and CSS of your design into ThemesPress [?]
3. Replace parts of your HTML with a few short tags
4. Set your presentation settings and preferences using our simple menus – and you are done.
Preview your design, edit it as much as you want, and if you like it, purchase it and download it.
Your new template costs a measley $10. After I created one for an existing site I just uploaded it and changed the permissions on the template files. I did this because I knew I needed to edit the style sheet afterwards because I generated the template fast for editing later. So, here is a theme I created using themespress for a photography site of mine. See how nice it matches the rest of the site. Anyway, if creating your own wordpress theme is something you've been wanting to do then now is your chance. Give it a try, I think you'll like how quick and painless it is.
If you do use themespress to create a wordpress theme then use Internet Explorer since Firefox has some problems when trying to preview the theme at the end. I created my first theme in firefox without any problem but the second gave me errors and then after viewing the theme in IE it showed up all weird. So just start in IE, even though you may hate it.
Also, make sure you have all your html just how you want it because you can't edit it later, only the css. So if you do create your own theme and find out later some of layout is missaligned you can go in and still tweak your style sheet.