Hope I can help a bit. First of all, I've always used Kawaks for Metal Slug ripping. Has some very useful tools, like the tile viewer and the shot factory. (Maybe MAME has these too; I'm not too sure. I remember always having bad experiences with MAME as far as sprite ripping tools; that's why I always stuck with Kawaks.)
As far as I know, there's no way to just directly rip them from the files, though I wish it were that simple. For almost all Metal Slug games, you'll have to go through manually and rip each sprite within the regular gameplay, or using the tile viewer. This is tedious and sucks horribly, but it can be made easier in Kawaks by eliminating all layers except the sprite layer; if you need to go further than that (for example, the backround being within the sprite layer), the shot factory lets you eliminate each sprite individually.
However, one of the games in the series makes it extremely easy to rip sprites, and that's Metal Slug 5. Contained within its debug menu are 2 sprite viewers that will let you view literally every sprite in the game without having to go through the hassle of using a tile viewer or gameplay itself. Essentially you set the game to console mode and turn on "developer mode" and you're able to access a level where it simply shows you all the sprites individually with a pretty much blank background, making ripping very easy.
I'll try to run you through it step-by-step.
1. Go into Kawaks
2. Game > Neo Geo settings...
3. Check both "Console" and "Developer mode"
4. Start Metal Slug 5, get to the character select screen and hit the Coin button twice to bring up the debug menu
5. Select the third option on the list, which will be all in Japanese
6. This will bring up a list of levels to start from; go to the third line and press backwards (left) once or twice to get to either "D T_5" or "E T_6".
7. D T_5 is the sprite viewer that shows all the main sprites of the 4 main characters, and E T_6 is the one that shows every other sprite in the game.
8. You'll select your character normally, but the level you enter will contain sprites in the center of the screen you can scroll through by using the main buttons, and a blank background. Perfect for sprite ripping.
Hope this helps.
As far as I know, there's no way to just directly rip them from the files, though I wish it were that simple. For almost all Metal Slug games, you'll have to go through manually and rip each sprite within the regular gameplay, or using the tile viewer. This is tedious and sucks horribly, but it can be made easier in Kawaks by eliminating all layers except the sprite layer; if you need to go further than that (for example, the backround being within the sprite layer), the shot factory lets you eliminate each sprite individually.
However, one of the games in the series makes it extremely easy to rip sprites, and that's Metal Slug 5. Contained within its debug menu are 2 sprite viewers that will let you view literally every sprite in the game without having to go through the hassle of using a tile viewer or gameplay itself. Essentially you set the game to console mode and turn on "developer mode" and you're able to access a level where it simply shows you all the sprites individually with a pretty much blank background, making ripping very easy.
I'll try to run you through it step-by-step.
1. Go into Kawaks
2. Game > Neo Geo settings...
3. Check both "Console" and "Developer mode"
4. Start Metal Slug 5, get to the character select screen and hit the Coin button twice to bring up the debug menu
5. Select the third option on the list, which will be all in Japanese
6. This will bring up a list of levels to start from; go to the third line and press backwards (left) once or twice to get to either "D T_5" or "E T_6".
7. D T_5 is the sprite viewer that shows all the main sprites of the 4 main characters, and E T_6 is the one that shows every other sprite in the game.
8. You'll select your character normally, but the level you enter will contain sprites in the center of the screen you can scroll through by using the main buttons, and a blank background. Perfect for sprite ripping.
Hope this helps.