Sorry for this simplistic question...but are these cameras the same? Did one came out before the other? If you have a GY-HD100 does it mean that it is in fact a GY-HD100U.

The reason I ask is that I am planning to purchase a second camera to use as a second camera for the one I currently own...but i asee all these GY-HD100U's but my manual say I have a GY-HD100...I'm confused

There is no difference. Sometimes the documentation drops the "U" or "E" because the European english text is mostly identical to the American.

The important thing is that the "U" shoots standard def in NTSC and "E" shoots standard def in PAL. The HD modes are identical around the world.

Not to confuse you further but all HD100U cameras should have been updated to HD100U(A) either at the factory or during the free update period in 2006. You will know if it is if there is an (A) sticker near the serial number on the bottom of the camera.