/give is a command on SMP servers with specific server wrappers. Inventory editors do the same thing but in single player.
If you don't want to go through the hassle of modding your Minecraft.jar, I would reccomend INVedit.
If you want ease of access, you may want to use TooManyItems. I guarantee you it will not steal your password.
For all it's worth, though, I don't see why you don't just use INVEdit or TooManyItems mod. It's great that you're trying to be careful, but you'll never see the sun shining if you're constantly holding your umbrella because you're afraid of the rain. I have INVEdit, and there's no viruses.
Also, a mod is an extra bit that you add into the game's coding that changes the way the game behaves. TooManyItems mod lets you edit your inventory while inside the game. A 3rd party program is a program written by someone who isn't affiliated with Mojang. INVEdit loads your inventory from Minecraft saves, lets you edit them, then lets you save them back into the game, all of which taking place in a separate window outside of the game. Minecraft shouldn't even be running when using INVEdit.
Will someone plz accept that ima noob and explain what the difference between an external 3rd party program and a mod is?
The program doesn't involve messing around with extracting minecraft.jar and is pretty much impossible to mess up.
Mods can break everything even if they are non-destructive just by being installed wrong. I wouldn't worry too much about mods stealing passwords or anything as long as a quick look at the thread for that mod doesn't reveal a bunch of people saying "This mod stole my password", but you'll want to be careful during the actual installation.