Follow this and your userbar can look like this:

1) Open up GIMP and then go to file and hit new. Your width should be 350 and height 19.
2) Pick the colors you want to use. (Border, scanlines, background, and etc.)(I used a light red and a dark red to gradient it.)
3) Add your border. For this userbar I used 000000 for the border. Once you click on the userbar to make your border you can hit shift after letting go on the mouse button to create a straight line.
4) Add your scanlines if you are using scanlines. Remember that scanlines shouldn't be really notice able. I didn't use scanlines.
5) Add your renders and make sure you Anchor the layers down.(I used three renders to make this one.)
6) Add text. Normal font for userbars are Visitor fonts. If you don't have it do a google search on Visitor Font and you can get it that way. It should come with Visitor TT1 BRK and Visitor TT2 BRK. I suggest using Visitor TT1 BRK at 20px.
7) Merge your text to the userbar.
8) Click on the circle tool on the toolbox and then drag it to make it the size you want to use it at.
9) Click the dodge/burn button on the toolbox and make sure it is on. You will have three different settings you can put it on. I suggest using shadows and midtones together.
10) Now go back and redo your border since your images maybe hanging on the edges of them and where you did the dodge at.
11) Go to file and save and save under the name you want it. Now your userbar is finish and it should look like something close to my.

Please post your userbars up after you do this because I would like to see how well this Tut did for y'all.