Redirect external traffic to internal sharepoint page

Yes, well, if I try to go just to http://sharepoint I don't get anything, I have to go to http://sharepoint/sites/dm/default.aspx. Internally we have a DNS record that points 'sharepoint' to the load balanced front end IP (using Windows NLB, which the F5 will replace sometime in the near future). Given that I am changing it from http://donor.company.com on the outside to http://sharepoint/sites/dm/default.aspx on the inside, do I need to change the host name AND the URI in two different steps? Not sure how to combine those in an iRule yet. Excuse my ignorance, the F5 is brand new to me.