Metroid Password Generator
This form comes in three versions: plain HTML, simple JavaScript, and Ajax. The plain HTML version is a standard, boring form. The JavaScript version is the same, but with a few extra (and handy!) features, like a button that will select all missile upgrades. The Ajax version will display the current password at the top. (Ajax is a particular feature of JavaScript, but not all browsers with JavaScript can use it.) The code was carefully written so that the appropriate version is automatically selected. For example, in Mozilla Firefox, if JavaScript is disabled, you'll see the plain HTML version, and if it's enabled, you'll see the Ajax version.
JavaScript is disabled (or your browser isn't compatible), so you're seeing the plain HTML version.
If the code generated doesn't work, make sure you didn't confuse 0 (the number) and O (the letter). Metroid's font gives the letter O a dot in the middle, which was traditionally done for the zero, making them easily confused when you're entering a password quickly. (Most generated passwords won't have a letter O.)
Note that this generator cannot generate all possible passwords. However, it will generate most practical passwords, and it will not generate any passwords that make it impossible or extremely difficult to complete the game (other than by setting your location to Tourian with no items or something). Many of the passwords that cannot be generated aren't very useful anyway, such as passwords that remove the Morph Ball from the map but do not give it to you, making the game impossible to complete.
In the normal game, it's impossible for the Ice Beam and the Wave Beam to coexist, but they can through passwords. The result is an Ice Beam that uses a blue Wave Beam sprite. It doesn't seem to behave any differently from a normal Ice Beam.
Note that you can specify that Mother Brain is defeated. If you do this, the game is normal until you reach where Mother Brain should be. When you get there, you will see the message to evacuate (it will look like it's part of the background), but the time bomb will not activate and you will have an infinite amount of time to exit Tourian.
Are you familiar with the famous "Justin Bailey" password? It is the most famous password which gives you "suitless Samus", with Samus in a leotard instead of her Power Suit. (Some interpret it as a swimsuit, but typical swimsuits don't have sleeves.) The top row is "JUSTIN BAILEY" and the second row is all hyphens. Nobody knows who came up with this password, but, believe it or not, it wasn't intentionally put there by the programmers. It is pure coincidence. Unfortunately, because of the way this generator works, no combination of settings will result in the famous "JUSTIN BAILEY" password; there are other Metroid password generators that can do it, though.
One password that _was_ put there by the programmers is "NARPAS SWORD". Just enter "NARPAS SWORD" and hit Start. (Technically, it's "NARPAS SWORD0 000000 000000"; hitting Start before completing the password fills the rest with zeroes.) The password is probably meant to be read as "NAR password" and not "Narpas Sword". Nobody knows for sure what NAR stands for, although the most common theory is North American Release. (The password system was first introduced in the North American version, since the Japanese version used the Famicom Disk System.) Another plausible theory is it stands for the last name of Tohru Narihiro, who designed the password system. The password gives you all items (including Ice Beam and Wave Beam simultaneously), infinite energy, and infinite missiles. You still have to beat Kraid, Ridley, and Mother Brain yourself, though.
Thanks to John Ratliff's Metroid Password Format Guide for the information. I also used his Metroid Password Generator (only the program, not the code) as a reference to make sure my generated passwords are correct.