You need to insert the e-mail code into an image to make it work. The one you copied is the HTML code. It's much easier to make the button when you are in the WYSIWYG mode. To use the WYSIWYG mode, click on the button on the top right corner of the quick reply box where there are two 'A's. Here's an example of a Buy Now button I just made:
To make one, follow the same steps you did to get the HTML code, but this time, copy the e-mail code. Copy the image link of the button and put [IMG] tags around it. Then insert the e-mail code and you're done.
Having any problems? Ask away.