If you want to upload pictures from your hard drive to a picture hosting service, you can use:
http://imageshack.us/or my service:
http://5g8.net/uploader/ (user ID and password are both the word
test)
Both services will format the url with images tags so you just have to copy and past the code provided; you don't have to add any more tags to it.
For example:
On my service (similar with Imageshack) just click on Browse and a window will open that will allow you to find the file on your computer.
Once you have selected the file, click on Send File (it defaults to add the image tags, so you don't have to bother with that).
You will then get the code returned in the small box, with the image tags already inserted; just copy and paste that code into your post.
As an example I have uploaded a picture and the code I get back will look like this:
[img]http://5g8.net/uploader/12294660739919_indyhathole23.jpg[/img]
Which will produce this: