It happens to me with older games, like X-COM : UFO Defence and Total Annihilation - and it makes these classics unplayable.

When I run these games, they work perfectly well, as far as playing goes, but they have an incredibly irritating black flicker, which means that I can't stand to even look at the screen.

I have an LCD monitor, but I imagine that it's something to do with the refresh rate...

Any ideas about how to stop this?

Try messing with the refresh rate in your display properties?

In which enviroments does this happen?

It happens with older games, I don't know enough about computers to tell you anything more than that.

It might be that my version of Direct X isn't old enough to support these games, is there any way to, say, install Direct X 5 over Direct X 9.0c so that I can have the older Direct3D files?

No.

It doesn't have anything to do with DirectX version. I guess you're running the games in DosBox under Windows XP. Windows XP has a known problem with using the basic refresh rates of the resolutions for applications/programs, eventhough the refresh rate for the monitor is set in Windows XP to a high value. Might be that they didn't fix that even in new follow-ups of Windows XP - Windows XP 64bit and Windows Vista.

There is a way to help that, though, but it requires you to set some values in the registry which is anything else as recommendable for you as you seem not to know much about computers. But there's a program that sets that for you, only rune it once and it finds the correct resolutions and refresh rates of your monitor out, setting the refresh-rates then to their highest values. In Windows XP AND in applications / programs. You can get the program here - RefreshForce

No, I'm running them in XP, and they're the windows versions of the games.

I also know that my monitor should be at 75Hz and that's what I've got it set at, which is what's making it so infuriating.

I was talking about DirectX because on the Total Annihilation discs it gives you the option to install DirectX (probably DirectX 3 or something) and when I clicked on that, it brung up a little window checking my DirectX version out, and for the Direct3D version, it was supposedly missing data.

Moved to technical.

I use DX9, I have XP SP2, I have refresh 85hz.

Chances are its not XP or DX. It could be your card not liking older games, or your LCD monitor...

Aye, it's probably my card, sadly. Oh well...

I have DirectX 9.0c @ 75hz, XP professional SP2, nVidia 6200SE TC (256MB)

and every thing works fine :P