What do you mean by version control?
Do you mean by which palette you are using in your present game?
Or to get your sprites to appear as they should with ack's default palette?
All sprites (tiles) will appear as dictated by a palette. Ack has a default palette, but you can add your own if you put in your game folder a .BMP image that contains all the colors indexed by which you sprites need to appear.
I think it is titled palette.bmp but can't check it right off hand.
If you need things to stay the same color indexes every time you add a new tile then I would convert every new tile (placed in the import folder) to the official palette you end up choosing for your game. Be it ack's default or your own.
If you have more questions about what I just said please tell us.
Also if this doesn't help please let us know what you mean.
Once you have an "official palette" image. all additional tiles added to your game will need to be converted. It will be a step you will always take to get new tiles into your game.
Converting to the color index so that they appear as they should.
If on the other hand, you mean the sprites you are appending are not of the necessary 16x16 pixels, then you must find a way to get each of your sprites to look as they should 16x6 pixels. This can be a challenge with paint programs as when they shrink tiles they end of blending and bleeding is such a fashion as to not work right. Sometimes you can cheat, as garth mentioned in another post, by ctrl+- to shrink images in a browser window, then use print screen to snatch the new size of the sprite. This still isn't always perfect, but helps a good deal.
What I do is shrink a sprite (knowing what it looks like in regular size) and then draw the same tile in a new layer on top of the old one. I simply draw a new version around the general layout of the original which no longer looks right being shrunk and all.

This might work:

http://www.alferdspritesheetunpacker.fo ... nload.aspx

And I really need to get my sprites into some sort of version control.

I was making a reply but then my OS crashed half way through. Instead I made a tutorial for converting tiles to one ACK can or is using. With screen shots of the program called MT Paint.
What I would do in your case is to load this new tile sheet into a better paint program then MT Paint, and divide all of its tiles into separate images that are each 320 x 200. Then use MTpaint to convert them all to the palette you are using. You can also convert them to ACK's default palette.
When I get a tile sheet from another game, this is what I do. I rearrange them to fit several 320x200 images and then convert each of them using MTPaint.

Hey guys,

I bought a tile set from Oryx Design last night. It’s got slices that are gifs, pngs and PSDs. It also has some “sheets” that are pngs.

What’s the recommended way to get these graphics into ACK?

I am OK with doing one graphic at a time. If it can handle a sheet, that’s cool too, but I doubt the sheets are compatible.

(When I try to import any of the graphics as a .gif, I get a garbled image, as if each pixel was a random color. I am guessing I need to convert them?)

I guess my first questions are:

ACK creates 320x200 games, right? Is that the max resolution?
What resolution should each tile be?
What is the process that I can use to import a graphic, down to the literal mouse movements I would need to make?