I have put Ubuntu on my mum's desktop computer. Unfortunately, the open source radeon driver does not work well with the onboard ATI graphics, and ATI's proprietary driver no longer supports the hardware at all. In order to use the ATI proprietary driver with this hardware, it is necessary to use an older version of Xorg, which is now only available in versions of Ubuntu older than 8.10. Unfortunately, the open source radeon driver seems to be causing X to lock up intermittently when my mum uses Audacity.
I'm willing to accept that some hardware is not well-supported on Ubuntu, and so, because this is a desktop computer with a couple of free PCI slots, I think a better solution might simply be to plug in a new graphics card that might have better driver support, and to disable the onboard ATI card in the BIOS. The requirements for this card are that it be inexpensive and have robust (preferably open source) driver support in Ubuntu 10.04. Heavy-duty graphics processing power is not a requirement. A second-hand card on Ebay would also be fine. Can anyone make some recommendations?