Unfortunately, ATI does not support the Mobility graphic cards from Dell, and you'll be forced to download a small verification tool before download, which will ultimately reject your desire to download.
you can take stu's advice and get the Omega's (quite good), or if you are only slightly more daring, you can go here
and download the mobility modder, and then go here
and get direct access to the latest ATI drivers without the hassle of being denied.
just follow the modder steps from step four onward, and you should be very good to go. I'm currently using the latest 7.10's with this method, and I had no trouble.