There’s a free theme generator HERE. I’ve never used it so I have no idea if it works or not or how well it works.
If you have a fairly simple theme plan, I say go for it (and let us know how it works please?), but if you want something more complicated in mind…
In spite of me linking you to the program, your best bet IMHO is, like Gangleri said, to:
1. peruse the library of themes given in the link (and there are a LOT of really nice themes of all colors, layouts, and sizes) and find one that is closest to what you want and just leave it as it is,
or
2. once after installing the theme that suits you best, to fiddle with the files and change the colors and header image (and whatever else) to display how you would like it to,
or
3. ‘hire’ someone to do the code alterations for you.
I suggest this because:
It is of my opinion that WordPress is a bit notorious for being more difficult to stylize/theme from scratch and this is coming from a front-end web developer who’s done this sort of thing for several years.
To really be able to create your own theme from scratch, you need to understand PHP, WP-specific coding, and XHTML and CSS. More importantly, you need to understand how it all works together.
Additionally, WordPress is not just a landing page like MySpace is. WordPress is a whole site – the whole kit and kaboodle – and you have access to everything and will have to stylize everything if you want the site appearance to stay consistent.
For this reason, I believe that a theme generator for MySpace or Livejournal is not the same as a theme generator for WordPress. A theme generator for WordPress has more files and more coding to work with and the potential to mess things up or to forget to style something consistently is higher.
Not to say that the generator doesn’t work because it sure might!
I just happen to feel that utilizing someone else’s theme (which has been safely debugged for public use and distribution) and/or making necessary changes is more foolproof and probably will have a better overall personalized feel to it.
… But of course I could be wrong.