When you have outbound links on your website, (outbound links are links that lead away from your site to another site) you should always have them open up in a new browser window. That is so visitors can stay on your site longer and dont have to push the back button in their browser to come back to your website. With links that lead somewhere else in your site you should not have the link open in a new browser window. You should also set all your outbound links to nofollow. Google likes sites that use outbound links to reliable sources. For instructions on how to nofollow your links go here.