I doubt that there will ever be support for importing SGDK1 games into SGDK2. The formats are too completely different.
As for framesets and tilesets: A frameset is a group of frames. Imagine a frame as any single graphic you have drawn, blasted onto a piece of stretchy, clear plastic. You can turn it around, scrunch it up, or stretch it out. You can also turn it upsidedown, etc. Basically, you can transform the graphic in any way.
Now, a tileset is a group of tiles, obviously. A tile is a collection of frames. These collections are useful for a few different things. Imagine an animated television show, like The Simpsons. They don't completely redraw every single frame of animation for the whole show. That would take way too long. Instead, they have the background frame (for example, the kitchen), which they stick in the back, then they have each of the characters in their own frame, all layered on top of each other, to end up with a final animation cell. That's what a tile is like. Several frames layered on top of each other, so you can use different graphical components all together in one tile (that goes onto the map) without having to actually draw each variation separately. This way, you can have many fewer actual graphics (which take up a bulk of the physical disk space) and still have a plethora of tiles.
Tiles also represent full animations. That's where the repeat count comes in. If you have, for example, a background frame, B, and two foreground frames, 1 and 2, which represent two frames of animation (say, for example, mouth closed and mouth open, to animate a person's face talking), then you could create a tile like this:
B1B2
Where B has a repeat count of 0, and 1 and 2 have a repeat count of X. This way, B will show up with 1 on top of it for X frames, then B will show up with 2 on top of it for X frames. It's like having the kitchen and Homer standing there, then having the kitchen, and homer sitting, and it would animate between them. Of course, in most cases, you'll probably have more than just two-frame animations, and they don't necessarily need to have a background in the tile. The animation could have a clear background to see the layer behind it through the animation.
I hope I've helped. Just ask if you don't understand something.