I hope you've got a working backup of your database somewhere, because if the download system has modified the tables structure, you're screwed.
Perhaps the version of ecDownloads you installed isn't compatible with your version of vBulletin ?
Here we use paFileBase that is completely separated from vBulletin, it has its own database. I had to manually reskin it so that it looks like the forum, but as a result when one of them breaks down, not all the site is unusable.
As for your vB hack, personally I wouldn't bother, I'd look directly into the PHP for the BB code replacement function (can't remember where it is, I believe it's in one of the inc_blablah.php file) and change around the [ img ] tag. Just change <img src=blabla> to <img width=X height=Y src=blabla>.