Here's how to install a nifty little program called Navigation Popups, that lets you peer into Wikipedia articles when you hover the mouse cursor over internal links:

• Quick installation: Enter Special:Preferences and click "Gadgets", check the box to enable Navigation Popups, under the "Browsing" section, then click save. Follow the instructions on the page to bypass your browser's cache.
• Other installation method: add {{subst:navpop}} to your current skin's .js page. See Wikipedia:Tools/Navigation popups#Installation for full installation instructions.

For this to work, make sure you have not disabled javascript in your browser. By the way, Navigation Popups is recursive: it works on links that appear in its popups.