Paint is Microsoft paint. It doesn't support the invisable pixels, and not very good for skinning. There are many skin makers around the web, or paint programs (GIMP, Paint.NET ext) that are all allowed for skinning. [The armories on places like MinersNeedCoolShoes and Novaskin aren't allowed but the 'editors' are] Theres the Skindex editor, Novaskin, Minersneedcoolshoes, and MCskin3D made by Paril as far as I know that make skins.

Miners makes 1.8 only skins, NovaSkin makes 1.7 skins only [theres a 1.8 beta version], and the Skindex makes 1.7. MCskin3D can make mobs, 1.8 and 1.7 people, and models and such. There are tons of things you can use.

Heres links for you to try your hand at.
Novaskin MinersNeedCoolShoes Skindex Just remember, dont use part pickers or parts of other people's skins. [Like if I were to take the creeper scarf from Nakurex's Creeper Boy skin, and put it on Sugarbun's skin then post it] It'll get you banned and such..But yeah. And theres also MCskin3D made by Paril [as I said] that is a bit hard to get working, but very much worth it. [Read the desc, don't use the "Install mod" button] I, personally, use MCskin3D. Its a very good program for skinning.