use imagecache thumbsnails instead of imagefield so as to define a custom thumbnail size in the admin part of image_field

I know that it is a long debate. But i am not a programmer. I've applied two patches that doesn't work (I suppose because of the version of imagefield wasn't targeted by the patch)
I want to make a simple thing that I think lots of people want to do.
Have bigger images that these 100x100 thumbs by default and be able to setup these dimensions.
It seems clear, that it should be preferable to use the imagecache functionnality for that, but how?

Is there a module,
Is there a patch
Is there a theme trick that allow people to do so.

Thank you
Seb
http://blog.archizone.fr/