I'm having texture troubles with the first MDK game, some of the textures will randomly flash or disappear entirely. I've tried running the game with MDK_soft, but the textures look weird and have multi-colored streaks in them.

The flashing and missing textures is a known issue with the D3D version of the game, especially when it comes to nvidia graphics cards. Something to do with not supporting very old DirectX instructions I think.

Software mode should work fine and you also have the option of the 3DFX mode. Not sure what you mean about the multi-coloured streaks, though. The game does have quite a different kind of look to it, so what you are seeing might be normal. Care to give us a screenshot so that we can see for ourselves and let you know if it is correct?

This is the best one I could get, print screen just gives me a black image with the weird streaks.

Hmm, can't really tell from that, as you say, the print screen doesn't capture it correctly. You could try using fraps or similar to capture a screenshot. Or at worst a photo then uploaded.

In any case, if those purple dots are what you mean and they are that colour then that isn't right. GOG's screenshots include some from the start of the first level if you want to compare it. They are the newsflash, the avoid the radar and the second screenshot with the red floor. Others are from the first level too.

Have you tried using the 3DFX option instead of software mode?

OK, I had to install the 2.0 version of the game, but it worked like a charm, thank you.

Ah, yes, the 3DFX mode was only added in the version 2.0 installer. Glad I could help. :)

Oh, just one other thing. You might want to look at this thread about the 3DFX version.
http://www.gog.com/forum/mdk_series/mdk_censored_blue_particals

I've listed a fix for it there already and I've been in contact with GOG support who are looking into it.

You'll want to redownload the game as GOG have updated the 2.0 installer and it now has an uncensored 3DFX mode.