Hi. took a while, but finally got there.
It requires a bit of copy and paste but here is my answer in Drupal hope it helps. Note that Ubercart handles imagecache profiles settings or views, so that if you go to your imagecache display settings you will see that the displayed teaser etc are set on hidden, this is not the problem. To set your images up in Ubercart go to ubercart settings but thats still not the problem.
See my post here (full post http://drupal.org/node/938776)which refers on.
Specifically:
Finally; got somewhere. Figured if the preview was not showing, then nothing was going to work properly. Went back to bug reports and there is a host of unsolved reports on imagecache.
http://drupal.org/node/536596
http://drupal.org/node/371195
http://drupal.org/node/410200
http://drupal.org/node/359387
And much more!

I figure its a Windows server issue based on 410200 above and the key was modifying (about) line 320 imagecache.module CHECK THE OP first:
return url($GLOBALS['base_url'] . '/index.php?q=' . file_directory_path() .'/imagecache/'. $presetname .'/'. $path, $args);
Now if you refer back to my site the images are all there. Thanks for the help.

In summary, there was no need to make any changes to .htaccess or permissions in my case.
Also, make sure you flush your imagecache profiles after applying this code. Also would make sense to do an /update.php because if you dont, it may still seem flakey.
Kind regards,
Alistair.