Ok...I've made a few of my own brush packs lately...they are alright and have used them in my recent sigs..so heres how I made them!
1. take/get a picture. I took a picture of my deck in my backyard (made of wood) so it worked out well. For this tut I will use this picture
2. Open it up in Photoshop. If the picture is a large picture (1000+ x 700+ Pixels) then you might want to resize to like 800x___ or whatever because you don't want the brushes to be that large..if you plan on using them for a signature.
3. Desaturate the picture (image>adjusments>desaturate [Shift+Control+U])
4. Mess around with the brightness/contrast(image>adjustments>brightness/contrast)of the whole picture until you get something similar to this.
5. AFter doing so, pick your rectangular marquee tool or your polygonal tool (recommended) and set your feather to about 10-15 px.
6. Select and area you want to make into a brush and make the polygon/rectangle around that area.
7. Select the brush tool and select a pack with very little brushes in it and delete all of the brushes in that pack (don't worry they will be there after the tut is over).
8. With your area still selected go to Edit>Define Brush and name that brush (I just name mine: 1, 2, 3, etc..) and click Ok.
9. Go to your brush selection area thing..and click the arrow in the upper right corner and click "save brush"
10. Name the brush pack and save it under MyComputer/LocalDisk/ProgramFiles/Adobe/Photoshop7.0(CS)/Presets/Brushes/AdobePhotoshopOnly.
There ya go..you've made a brush!..Now go make more!
PS: You can make multiple brushes and then save them all..You don't have to make one then save it everytime.