Creating a template for version 3 isn't that difficult, just take some time to look at the default template and understand how it works.
When creating your new template, remember to create the admin/includes/templates/template_name.php file to let the admin section know there is a template there (you can just copy the default one and change the contents to reflect your template).
If you want to take a look at some of the templates I've been creating to see what files are included or how I did it you can look at the site in my signature (this isn't an advertisement just citing an example that might help you out -- download one of the osCommerce templates -- it will include all of the file that need to be there for a new template).
Though it's not that hard, it took me a little while to fully understand the template system ... now that I get it, making new templates is a breeze.
Good luck
