Hello! Have you ever thing about playing Portal with a custom portal gun? Now you can do this, just follow me step by step, alright? Okay, lets begin!
1. Download and install VTFEdit from [here](http://nemesis.thewavelength.net/)
2. Go to here (Portal's folder): `Portal\portal\materials\models\weapons\v_models\v_portalgun`
3. Open "v_portalgun.vtf" file with VTFEdit.
4. Now you see the portal gun's texture. Press a right click, and click on "Copy".
5. Run a picture-editor, and paste it in a new picture.
6. Edit your portal gun.
7. Save your texture in a PNG file.
7. Open simple VTFEdit: File -> Import, and select your portalgun texture.
8. Save it to "v_portalgun.vtf", and drag it into the v_portalgun folder and overwrite it.
10. Start Potal, and if you did it right, your re-textured portal gun is in your hands :)
Thanks for reading, and I hope it works for you.
P.S.: Yes, my English is poor, and I'm new here!
My blog: http://www.gposthu.tk
My Portal Fan Page: http://www.portalhunfans.tk
May I recommend copying the edited texture, and pressing Ctrl+V in VTFEdit instead of importing it? That saves time for me. (If not using the BGR888 or BGRA8888 format, saving the file somewhere may still be a good idea, if one wants to edit the texture further later.)