Ah, you're using vB4? Probably would've been wise to say that, and also post a screenshot of what you wanted in your first post, since vBulletin.org is running a completely different version (3.6.12) than you are running...
Anyway, add this to your additional.css template:
PHP Code:
.navtabs li a.navtab {
margin: 0 35px 0 0;
}
Also, change
35px to whatever you want