I know i can already do it, but it takes a lot a time !
The height and width metadata has to be read from each file in order to sort by that data. Indexing the location should allow for much quicker sorting. Is the folder in question already indexed (use the Indexing Options Control Panel item)?
Can I just permanantely add "dimensions" in the sort tab ?
You can add the Dimensions column in Detail view and then click "Apply to Folders" in the folders properties dialog in order to set that view for all other folders of type Pictures (or possibly all folders of type General Items if you're on a removable drive).
If you can't get the desired settings to stick, you should be able to get the desired results using my free WinSetView app: