MAME system video issue

I haven't been able to put much time into trying to fix this yet, but I have one odd problem with my MAME system's configuration that I thought I'd post about in case anyone had any ideas. It's not a showstopper, and oddly it doesn't seem to affect the games themselves very much (though I haven't tried many), just the Windows system you use to select them.

The computer is a ASUS Eee Box HD 1006 Nettop PC which uses an HDMI port for its video out (and no other options, though it does include an HDMI-to-DVI adapter), and ATI Catalyst Control Center for its video software. The monitor is a Vizio 22" 720p LCD HDTV whose native resolution is 1366 x 768. The only information I can find about what video it supports is the following:

• Signal Compatibility: Supports 480i (SDTV), 480P (EDTV), 720P (HDTV), 1080i (HDTV)
  
• Colors: 16.7 Million
  
• Computer Support: 640x480, 800x600, 1024x768, 1366 x 768 via VGA

When I hook these up via HDMI, the video resolution that I get is 1024 x 768, which gives the video a jagged, uneven resolution in Windows. When I go into games, that jaggedness generally disappears since we're scaling up from much lower resolutions anyway; Tempest, for one, looks exactly as good here as anywhere else (that's not a vector monitor, I mean). But other games will probably get some artifacting from having the resolution scaled twice, and certainly Windows itself does, as does the MAME UI.

I've tried setting various other resolutions, even forcing 1366 x 768 and using the ATI Catalyst Control Center to manually tweak the size to match the resolution, but it never gets rid of the jaggies. It seems like it's a consequence of using HDMI to hook things up, and perhaps the native resolution is only available via VGA, but I'm not sure what I can do about it. This computer doesn't have a VGA port. HDMI to VGA converters are expensive, but even if I got one, I suspect that the same issue would arise. I wonder if this cable might help; it seems unlikely, but I am not sure what situation it would be helpful in if not this one, and if I can get it for a few bucks it might be worth it for the experiment.

It seems like a silly limitation in any case. The computer ought to be able to use the resolution of any HDMI device it plugs into, automatically. Maybe it would on most, but the oddity is in the monitor. I don't know.

It might be that the best solution is just to choose a front end to MAME that uses big enough graphical icons for the games that the jagginess is unnoticeable, and hides Windows entirely. I don't mind seeing the jaggies on the rare times I need to get out to do Windows updates or stuff like that. But I'm not sure if there is a front end that'll avoid the jaggies. And it's certainly an extra step -- MAME itself would be enough front end for me otherwise. So a true solution would be nice, if I can find one.