This technique was made in Photoshop CS2. I tried to make it in The Gimp but I couldn't find the same filters needed. If you can do it in Gimp, I would love to know.
Step 1: Open a blank window
Step 3: Add the Grain
Step 4: Rinse and repeat
If you don't have the filter repeat option (unlikely) then repeat step 3 three of four more times.
Step 5: Final touches
Finally, I want to make the wood seem more "hard." We're just going to "Filter > Sharpen > Unsharp Mask" and add a subtle sharpness to the grain. My settings were: Amount - 79%, Radius - 0.9 pixels, and Threshold - 0 levels.
Well, there's our finished woodgrain. I hoped you liked my 1st Instructable :D