Hi potterfan3,you can open a tab by pressing the Ctrl button whilst pushing new link or you can press Shift and open link in a new window,hope this helps...............
Does the middle button work like normal in other programs? Try opening internet explorer; the middle button usually changes the cursor to an up/down arrow so you can easily scroll up and down the page.
Do you have a third party mouse, such as a Logitech (cordless maybe), that has software that normally runs that lets you change what the buttons do? If so, run that, and make sure that the middle button is set for the default middle button action and nothing else.
Failing that, check Windows' default mouse settings, and make sure that the middle button is set to the default middle button action, if it's configurable.