TubeNet

You mean the "avatar" on the left? There's an option towards the bottom of the page you used to edit your profile. There's no gallery of avatars to choose from yet, but you can use your own, provided it fits the size requirements.

For an image in the signature, I think it can be done by using an html tag. I wouldn't recommend it, though -- each one doesn't really contribute to the discussion at hand, they take up more space, and if everybody had one, the pages would take forever to load on a dialup or cell phone connection.

Go to the very bottom of your profile. You should see something called AVATAR. That is the cool pics.

you can also have pictures in your sig file too... which is what I am going to do next...

Select an image that is saved on your hard drive (or coppied to your hard drive from whereever) and open it using any software that allows you to change the dimensions. Adjust the size so that it is no more than 80 pixels in height and width. Save that image as new file.

When updating your profile, at the bottom of the page you'll see the Avatar control panel. click on the BROWSE button to the right of where it says "Upload Avatar from your machine". Find the file you saved and select it. Then just click submit and you're set!