The programs you need to skin are GCFSCAPE and VTFEDIT and GIMPSHOP you can get these at www.nemesis.thewavelength.net. and gimp shop at www.gimpshop.com
After you get these programs, the first thing you want to do is open up gcfscape and vtfedit. (note exit all applicationsif you want to be organized and not get get confused). now click on gcfscape and click on file and then open, when you click open you should see like blues bokes of some sort and words next to it, now click on the blue box that says counter-strike source shared. now click the + sign that says cstrike then materials, then models then weapons then v_models. now the v models folder is a folder that contains the weapons and stuff that lets you see your weapon in your hands, the w models folder lets you see the weapon in the ground like the world view. now click on v models and click on the weapon that you want to edit. i will be showing how to edit the ump so now drag the weapon that says smg_ump45.VTF to your desktop, now the vtf part is important dont drag anything else than the vtf model of the weapon. now open your vtfedit and click file open, if you have vista then on the left side click desktop and find it there but if u have windows xp then go to desktop then find it then. when you found your model click on it. then you export it by going to file export then find the vtf and export it to desktop, then you open gimp shop and click on file open and open the weapon tga file then you should see something like this(screenshot A). now get a picture of a skin you would like to put on your weapon and drag that skin to your desktop then drag that skin on top of the background thingy, (screenshot b) then where you see the normal sign click on the overlay sign (screenshot c). then click and drag your image that u want to your gun(screenshot D) after that you click save as and i dont think it will let u save it but then it says to export it, so u export the picture to your desktop. then youopen up vtf edit and click file import and import the TGA (the thing you just skinned) then you click file save and then you find the tga file and you name it exactly as what you saw it as (screenshot e) then you go to your desktop and drag your new skin to your weapon folder, steamapps counter strike source cstrike materials models weapons v_models your weapon folder and drag the new vtf to your folder and there you go u just created a new skin BAM!!
Ouch. This isn't a good tutorial. Needs HTML, must have better screenshots, needs to be organized (hard to read a wall of text without any dots, slashes and numbers) and most important: English skills.
Improve this things and write again, We'll see.