Very nice pictures. Are you using the lens that came with the camera? I just picked up a XTi and some lens.
It's not that hard to use the manual settings. For action shots you should use the AV setting and set your aperture as wide as possible f/4 or lower and the camera will select the right shutter speed. Also set the AF to servo mode and follow the action to anticipate it.
Regarding RAW vs. jpeg. RAW is the actual picture that you took without any compression being made. This lets you adjust many aspects of the picture in post production. Whereas jpeg pictures are compressed somewhat and you can only manipulate some aspects of the picture.
I myself just started learning about the wonderful aspects of photography and the best thing is that if the shot is awful, you just erase and try again
Here are two pictures I shot of Angel. The first one is her chewing on her favourite toy and the second one is of her just leaving her feet to jump for a stuffed toy. It's a little blurry because I didn't focus just on her but the whole frame.