I am not sure, being dell they could be wrong but they also do get there own stuff made for them, I can not see this being incorrect with Dell. All I can say is if you have the laptop already, print screen it and talk to them, but if you haven't get in touch with ATI and ask them. I have done both as I have this card yet to test games.
I am sorry i can not help more! But i do remember notebook website have 64/128 on it's memory bus going a couple of weeks back.