Hey 300zx_9,
I've been playing around alot with rhino lately and I find that the easiest way to go about constructing complex surfaces such as hoods and wheel arches is by creating easily manipulable preliminary surfaces and then splitting them rather than trying to force surfaces based on splines. Although these preliminary surfaces may take several attempts to fit the prints when they are split, the final product is much more impressive. If you'd like I can try to construct that hood with some pictures to show you what I mean. Here is a particularly helpful resource; all you need to do is register and check out the full car tutorial... it's totally free
ARTC