This is a simple, yet effective way to edit your inventory using NBTedit.
1. Go to this forum and read how to get your save file http://www.minecraftforum.net/viewtopic.php?f=35&t=13239.
2. Put the file in somewheres easier to find (e.g. Your Documents).
3. Open NBTedit.
4. Find and open the file named Level.dat. (This should be in the first folder you open)
5. Go to the folder (In NBTedit) named Data.
6. Open player (Though this does not have the thing called 'Local Player' it is still it)
8. Visit the same forum to learn how to open it again, follow the instructions
Note: You can not use this to edit anything but your player.
PS i figured this out a few days ago, just posted it on the NTBedit forum and didn't get views