Great topic!
However I didn't find the solution of my problem:

I added some additional attributes and need to pass them into a table. The $node variable at myproduct.tpl.php contains only the fully rendered form so I'm not able to add a table there.

Please help..I'm searching and reading and try&error since more than 18 hours but didn't find anything that could help. Nor the Forms API neither custom themeing functions help...nothing!

Any suggestions are welcome: adding code to my modul (would be my prefered solution for providing a default theme) or a way through the template-files.

Problem by providing a default theme: the module just adds an additional product class so it doesn't provide an 'own content type'. mymodule_view()/theme() are totally ignored. Please don't referre me to any book (have the pro development book). I think I got lost in space cause I'm still a drupal noob.

Thx,
haggis

edit: got it working! see how 'admin/content/node' is rendered at ../modules/node/node.admin.inc

edit2: you can find a cleaner way using ubercarts tapir at http://www.ubercart.org/docs/developer/7512/tapir_tables_api