The appearance of a link is controlled by both the user's browser and the appearance specified by the developer, with the browser having ultimate control over the final appearance.
As a developer you can specify how you want a link to appear - but you must remember that the user may have set their browser up to override your settings.
In Dreamweaver do the following: -
1. Open the page for which you want to specifiy the appearance of the links
2. In the "Properties" box (usually located in the lower part of the screen under the page) click on "Page Properties"
3. A dialog box will then pop-up. Click on the second item in the options list "Links"
4. Modify the links to suit your requirements