nomodeset worked, thank you.
Although Dell and Windows show my adapter as a Radeon Express 1150, lspci give the following info:
[liveuser@localhost ~]$ lspci -nn |grep VGA
01:05.0 VGA compatible controller : ATI Technologies Inc RS482 [Radeon Xpress 200M] [1002:5975]
This chipset seems to be supported by the latest free driver from what I can tell. I am way out of my depth here. The instructions for posting a bug report might as well be in greek.
When I shudown F13 I get the same vertical lines briefly. How do I solve this properly so that I can install the software and have it work reliably?