Deviantart
Angryblue
I downloaded mine off angryblue. I also downloaded angryblue's fonts, which are pretty good for grunge pictures.
After you get the brushes you like, open the .zip file and select the .abr file(s). Extract the .abr files to any file that is easy to locate. Sometimes I put it on my desktop, other times I put it in my brush folder (should be similar to C:\Program Files\Adobe\Photoshop 7.0\Presets\Brushes\Adobe Photoshop Only).
Open photoshop and follow these steps:
Create a new document, any size, any settings.
1. Choose the Brush Tool. [B]
2. Right click your empty canvas.
3. A new window will pop up. Click the arrow (with a circle around it) at the top right of this new window.
4. After you click the arrow, locate and select Load Brushes.
5. Look for your .abr file(s) in whatever folder you extracted them to.
6. Open them. If you have multiple, repeat until you have loaded all of your new brushes.
7. Right click the document and scroll down in the new window. You should notice new brushes. Always use the Brush tool when using grunge brushes, because the Pencil tool will make things choppy. The pencil tool is good if you are using linework or tech brushes.