Well LiLo installation worked flawlessly! Unfortunately though, Salix won't boot anyway. It seems to get most of the way, but then hangs with a bunch of lines about Radeon driver, init something, pci_bus_driver etc etc (I think maybe it's trying to load Radeon drivers?

) and a row of images across the top that appear to be a corrupted copy of the boot menu image.
I tried Slackware 13.37 a little over a year ago and had the same problem - installs fine, starts to boot but never actually completes booting. Only difference is that with Slackware, the boot output left on screen when it froze wasn't all related to Radeon drivers, but a selection of devices (I remember kb/mouse were always in there). So maybe it's not graphics driver-related after all... anyway, I retried that Slackware installation at least half a dozen times with every possible combination of GUI choices and package selections (including full install) and got the same result every time. So I think I'll save myself the time and effort here and call it a day. Slackware and it's descendants clearly don't like my computer!
Thanks Adys and sojurn for your help, really appreciate it. All distributions should have such helpful communities
