DNS Question

Here is the problem I am trying to solve.  I have a domain on site mycompany.com.  I also have a external website that is hosted by a ISP that is the name of www.mycompany.com.  As of now, for people on my LAN, I have them go to the IP address of the website and there has been no problem up to this point.  The problem is that now they have put in some new functions on the website and they are all tagged with www.mycompany.com\event.asp.  Since they have done this, no one can access the events that are listed from the LAN.

I have put in external DNS servers in the IP settings but that has caused some problems with connections to the exchange server and is causing me more problems than it is worth.

My question is, if I put in my local DNS in the preferred DNS server space and a external DNS server in the Alternate, how can I force when someone utilizes the www.mycompany.com website for that to be run into the Alternate DNS but then have everything else go through the primary DNS for everything else.

Thanks