Thanks Lidex. Your posts got me onto a few things and indirectly let me figure it out eventually.
Just a warning for anyone else who tries... 'envyng' let me install ATI drivers, EVEN THOUGH they weren't compatible with my card, leading to my computer restarting by itself a few times. Whoops
Anyway, the result of that was that when it recovered it gave me an Xorg.conf file to fiddle with, rather than autodetecting each time. With some tweaking based on this article, I came up with this xorg.conf file, which is working for me.
Changing the section in "Display" let me change my resolution manually. Still can't see anything in "Display Preferences" in gnome though
Identifier "Generic Monitor"
Identifier "Builtin Default ati Device 0"
Identifier "Builtin Default ati Screen 0"
Device "Builtin Default ati Device 0"
Monitor "Generic Monitor"
Modes "1680x1050" "1024x768"
Identifier "Builtin Default Layout"
Screen "Builtin Default ati Screen 0"
And I was just getting used to squished blurry fonts. Having the resolution at its native seems... too clean