The easiest way to deal with the Y axis issue (ie: getting your meshes bloody feet on the ground plane) is to go to your friendly neighborhood graph editor. Once the graph is open, you need to check both hip and body, to see which value is off (while it is true that the hip is the root of a bvh file, some capture methods can put data where it doesn't belong, and the actual cause of the problem is the 'body'. Not often, but better safe than sorry). But let's assume the problem is with the hip. Select the hip either by clicking on the figure, or choosing from the body parts drop down. On the upper right of the graph panel, choose 'Y axis' from that drop down. Now, place your cursor at the left edge of the graph, press shift, hold down your right mouse button, and drag the cursor to the right. The graph window should be turning black. Just continue dragging until you reach the end of the graph (you might want to slide the scroll bar and make sure the starting end didn't shift. All you need to do to fix it is set the pointer in the black field, press and hold shift and R click, and drag the field until it is back to the start). If you look at you cursor, you'll notice that it's changed from a single arrow to 2 horizontal arrows. If you press and hold the left mouse button, you could drag the selected keyframes in the dark field up or down the timeline without changing their relation to each other. This is handy for moving a motion along the timeline without running the risk of creating impossible amounts of chaos. Leave the cursor in the dark field, and press left CTRL, and you will see the horizontal arrows become vertical arrows. Just press and hold left click, and you can drag the selected keyframes up and down in motion value, again without changing their relationship with each other. You will also be able to see how the character's position is changing, and once you have it where you want it, just release the ctrl and mouse and you can close the graph until the next time you need it.