Thanks for the reply.
I'm switching back and forth between a SVGA LCD and the arcade monitor (via a JPAC). I set the settings on the PC monitor, then switch to the JPAC (which is connected to the arcade monitor). I can't get the Soft15Khz to seemingly do anything. With the onboard Intel 845GL video, it won't even install (everything is greyed out), but if I put in a Matrox Millennium II, I can install/uninstall 15, 25, and/or 31Khz, but it doesn't seem to change anything at all. For the moment, I've ditched all the front ends and am simply trying to get mame to work on the NEOGEO (standard res) monitor.
I was thinking about going to a pure DOS box and ditching the TinyXP, but then I think the USB interface of the JPAC might be a problem, so I'm back to trying to make this work in the contect of a Windows XP mame setup.