Goop,

I would reccomend you start with the 125, you can get the 250, but as a starter bike your going to have more problems with fouling the plugs cause it gets loaded up, be cause your putting around on it. A 125 is fast enough.

On the Pre97 Frames, they were some sort of metal, not sure what type off hand, but you will notice a big weight difference with the newer frame, also the 97+ has better brakes, better suspension and is a better MX bike.

The 2 Strokes are alot less reliable if unmaintained, they need alot of prevenative maint. unlike most 4 strokes witch you can just add gas and go.

As for brand, starting out I would not worry about any of that, jsut get what is cheapest, get some good gear, and boots, and give it hell(well more like its going to give you hell)!!!!

Hope this helps.

Jesse