I saw your post earlier, but I was at lunch, and typing on my phone is a tedious chore...
https://help.ubuntu.com/community/RadeonDriver
Ubuntu specific, but it does go list the chipsets/GPUs that are covered by the open source driver.
However, checking the X.org page for the Radeon driver, (the open source driver),
https://www.x.org/wiki/RadeonFeature/
if you look at the chipset listing for the 4000/5000 series (the first link) they are a RV700 series, aka the R700 series, if you check the 2nd link, you can see the state of the driver for the R700... (scroll down to the table, and find R600/700 across the top.)
If you installed any of the more recent linux distros, you already have the driver.
ATI/AMD are focusing on the newer hardware, but the open source guys aren't, they are working on the older hardware.
Unsure about the quality/accuracy/rep of the source, but this link goes over the Mobility 4530 a bit in depth, i.e. what to expect.
http://www.notebookcheck.net/AMD-ATI...0.13972.0.html
Only thing I would point out, is dispite Linus Torvalds (spelling?) aim at making linux a PC OS, it runs on EVERYTHING, so it has taken 'root' in buisness areas, and hardware.
Gaming on linux is not new, but is just starting to gain steam over the last few years.
The Hardware can most likely handle it, but the drivers are what is needed to get there.
(I had an HD4850 in that 5600x2 I mentioned in a previous post, it ran Crysis max res/settings, and did it at 70fps (WinXP). BUT it was driver dependent, updating didn't always help, had a few times I went back to the old driver... In Linux MOST of the time, it's a step up. Very few times have I had to downgrade...)
And I've found several Mobility 4X00 users requesting help with setting up the video, there's more out there then you think.
If you decide you want to give it another go... I'm game to try and see if we can find the answers.
Barracuda