I've had success using modded drivers on a Dell before, but the ones I used are no longer available in the mobile version. Laptopvideo2go has some drivers that are supposed to work with the 8400M GS and Asus/HP-Compaq. You would have to do some reading on the install process. Here's a link to a short walkthrough.
http://www.laptopvideo2go.com/forum/...p?showtopic=33
And here's the drivers they say work.
http://www.laptopvideo2go.com/forum/...howtopic=16927 They list the mobile cards that they work on and yours is there, though you have to scroll way down to find it.
Make sure you read the walkthrough first, if not the faq's and such, you'll need to replace the nvidia inf file with a modded version.
Don't know if it works or not, but might be worth a shot.