Try: UB Designer and UB Animator. They are both online web-based tools for creating userbars. You can also use advanced graphics tools such as the freely available GIMP which has some nice tools such as a collection of pre-made color gradients and other graphics editing tools.
There's also the more popular non-free tools such as: Adobe Photoshop and JASC Software's PaintShop Pro. PaintShop Pro has a free x-day demo you can download from their homepage.
My advice is to go for the free tools first since something like a userbar isn't a very sophisticated or extensive graphics project.
As far as "code to paste" you'll have to find somewhere to host your graphics creation. My recommendation is some free image hosting service such as photobucket. Photobucket will host your images and provide an http link you can use to hotlink your images to wherever you plan to use them.