I'm confused! (OK, I've been up all night and I've just got to the bottom of a bottle of wine but I think I would still be confused anyway). It's the bit about 'posting an image onto a website' that confuses me. I'm not too sure about exactly what it is that you're trying to do. So I'll start with the easy end of things:
To save any website image to your hard drive, right-click on the image and select 'Save as'. You'll then be given the opportunity to decide where you want to store the image. (e.g. in the 'My Pictures' folder). You can also change the name of the file, at the same time, if you so wish.
It's now that I start to get a bit lost. Obviously, you can't just add your choice of picture to any website. It has to be a website which invites you to post pictures on it. The problem is that different websites will have different methods for uploading images. In general, however, if there's an option to 'Browse', you should click this button and then navigate to where you've stored the picture on your hard drive. Double click on the image file and then click 'Upload' or 'Go', as appropriate.
If you require more precise information, please post again and tell us which website (e.g.MySpace) it is that you want to place the image on.
Chris