hi, can anyone tell me if there is a soft-15khz equivalent for ubuntu. i know there is the groovyarcade live cd but i believe this does not support amiga or dosbox emulation which is what i'd like to use. thanks
No real need. You can just dump the modeline into xorg.conf and specify it as your default (or only) mode, or you can use xrandr to add/change things on the fly.
e.g.
xrandr --newmode "ATSC-640x480-59.94i" 11.958 640 664 736 760 480 484 492 525 Interlace
xrandr --addmode VGA0 "ATSC-640x480-59.94"
xrandr --output VGA0 --mode "ATSC-640x480-59.94i"
(substitute whatever your output in use is named for VGA0 - you can get a list using the command "xrandr -q")
You can also do split modes - e.g. one monitor running a conventional PC mode and another running a low res mode. This is very handy if you've got a normal PC monitor + an arcade monitor or are using a laptop (so you can keep the onboard panel active for debugging/troubleshooting). There was a bug up through at least 10.10 that causes major problems if you try this, but it was fixed by 11.10 (and I think 11.04).
I suppose somebody could package all this into a little GUI similar to Soft15k, but the fact that it's relatively straightforward makes it unlikely anyone will bother. I suppose somebody's probably written a shell script to do it. Then again, a lot of people seem totally unaware of the existence of xrandr.
In general, the drivers will let you do anything the card is physically capable of. If you're lucky, they'll even tell you what's wrong if you ask it to do something the hardware can't do (e.g. dot clock too low).
Anything you do with the command line xrandr interface won't "stick" across reboot, so you can just reboot if you mess something up. If you want something permanent, you can modify xorg.conf to specify the modeline and default mode.