The highs are different, yes, but if you get it from the street, untested, it's often cut with crap. Both of the substances. Pure methamphetamine has a warmer, more intense feeling than pure amphetamine. Also, the feeling is more natural, less as if it's chemically forced on you. The duration of the peak is shorter with meth, but a long plateau where you can't sleep follows, as opposed to amphetamine which doesn't really feel like peaking, but more like a 7 hour plateau, which slowly deminishes. I think a new user to both substances wouldn't tell the difference, but I could clearly tell them apart, since I had 3~4 years of amphetamine use prior to my first meth experience.
I wouldn't know if a capsule works, but dissolving in water and plugging should.