Hard coded links to categories not work with pretty permalinks

Hi

I am a wordpress newbie. I have create my own custom theme and the nav is just hard coded links to category pages:

index.php?cat=8

I am trying to get the pretty permalinks to work. The links to the actual posts work fine but now the nav is broken. Instead of linking to the category page it now just adds the category location onto the end of the post url (localhost/wordpress2/2010/11/bonkers/?cat=7) which results in an error.

Any help would be greatly appreciated.

Thanks!