Howto install ATI Radeon X1300/X1550 support on Ubuntu 9.04+ . It’s actually quite easy, just install the open source driver. Forget the support from ATI/AMD, it isn’t there. But the opensource driver is good enough.

First install the ATI open source driver following this howto: https://help.ubuntu.com/community/RadeonDriver

Then, don’t forget to enable the kernelmode setting, following this howto: https://wiki.ubuntu.com/X/KernelModeSetting

if you don’t have a /etc/default/grub , but don’t worry, that’s pretty normal (as mentioned in the kernelmode setting)