That is odd that everything else is working, but RuneScape isn't. I got a bit curious, so I started Googling and came up with
this.
Apparently quite a few people are having issues with both Ubuntu 9.04 and Windows 7 when trying to use RuneScape high quality mode. Here's a RuneScape
forum link to a similar issue.
I re-checked for your driver and ended up at the same page. Unfortunately, I'd like to make sure you've seen the cop-out by ATI regarding your GPU and Windows 7,
ATI wrote:
AMD’s DirectX 9 ATI Radeon graphics accelerators are not officially supported under Windows 7. If the user chooses to, they can install the ATI Catalyst Windows Vista graphics driver under Windows 7. Please be aware that none of the new Windows 7 graphics driver (WDDM 1.1) features are supported (as the Windows Vista level graphics driver is limited to WDDM 1.0 level support). Using the ATI Catalyst Windows Vista driver under Windows 7 is not officially supported by AMD, and as such AMD will not provide any form of customer support for users running in this configuration