is there a way to make brushes compatible with older versions of photoshop ?

I’ve recently gotten the newest version of photoshop in creative suite 4 but it’s fairly new so it hasn’t caught on very much so I was wondering if there was some way I could make brushes cs3 (and even cs2) compatible compatible with cs4 or is that something the authors have to do.
When I unzip the brush file, it shows the weight which is like 117 (insert computer weight units). But when I try and transfer it into the ps brushes folder, it shows that it weighs 0.