your post seems to be a duplicate of this: How well does an ATI mobility radeon hd 5650 work?

...also a quick google search suggests you should be fine using a newer ubuntu version ie. 11.04 or 11.10 but especially if you're new to ubuntu use the instructions from the link that 'Ryan' provides in his answer.

**EDIT: In your question it reads ubuntu 12.04. This version is in development right now and is supposed to be released in April 2012. If you want to be sure that your laptop works as desired and you want to avoid bugs I'd recommend installing either 11.10 or 11.04 and stay with it til a few weeks after the 12.04 release date.