I had a similar problem on my laptop (look at sig for model). Same onboard video chipset. I used redhat9 on my laptop, it detected everything automaitcally in the install, including video, only problem I had was that I was stuck in 800x600 mode. I was able to get it working in 1024x768 (the max allowed on my laptop).
To do this, I hate to say this, I have no earthly idea how I managed it. Here is what I did: I dl'd the latest video drivers for linux in rpm form from intel. Installed them. Started X, changed the setting in the XF86Config file. Restarted X, no luck, was 800x600. I then dl'd the tar'd file from intel for the drivers, untar'd it, followed instructions, tried X again, still no luck. Then I uninstalled the tar'd files and the rpm. I tried X again now. Redhat9 uses gnome by default, and at this point, gnome got stuck on its startup screen. So Alt+Ctrl+Backspace, put "exec startkde" in my .xinitrc file in my home folder (that starts kde as my X desktop) and Voila!! I had 1024x768. Yeah, that's what I did. (Driver being used was the i810 that comes with the distro)
I myself searched extensively on the web, and seemed alot of ppl were stuck with 800x600 in linux, some solved it with patches, some used a distro that worked for their laptop model, some used drivers that were being sold by a linux vendor. Anyways, sorry I wasn't of anymore help. But search the web using "855gm laptop" and maybe your model of the laptop. You might find a solution.