So I have a Canon T2i dslr and a canon 430exII speedlite that I use off camera. I have a transmitter that I bought from Cowboy Studio that works pretty great. In high speed sync, the flash goes off but I still have the problem with the black strip when I do any shutter speed over 1/200. I don't understand what I could be doing wrong. I have read and read and watched videos, but I still cannot figure out what I am doing wrong.
Most low-cost (say < US$50/set) flash radio triggers do not support eTTL or HSS. They are "manual-only" triggers. It the triggers/flash only have a single contact/pin they're definitely manual-only, because that big contact/pin in the center of the hotshoe "square" is the sync signal and that's the only signal that can physically be communicated.
There are, however, also a number of low-cost flash triggers with all five of the Canon contacts (or all four of the Nikon contacts) that are still manual-only--they may use the additional TTL contacts/pins to communicate the wake-up signal, but most probably are simply using pre-existing parts they can buy in bulk at a low price. Not all five of those contacts are necessarily wired up to passthrough the full hotshoe communication signaling required for HSS, eTTL, or remote power-level control from the camera menu.
IIRC, the Cowboy Studios NPT series of triggers is manual only, so the behavior you're getting is simply the way they work. You can't go over your sync speed. Triggers that would allow you to use HSS are going to be more expensive, and can typically also communicate TTL. A list of TTL and remote-power control triggers can be found on the Flash Havoc website; many of the TTL triggers also support HSS.
Unless the specs on the triggers you got specifically say they support HSS and TTL, I don't think you're doing anything wrong--you've just hit a limitation of manual-only triggers.