I have Metroid Prime 2.

Do I need to purchase, play, and beat MP1 in order to enjoy MP2? 

I think you'll enjoy MP2 less, if you play MP1. MP2 is not bad, but not better than MP1.

Nope. They are separate stories but linked mainly on two parts: Phazon and Dark Samus (Metroid prime).

you can enjoy in any order

There's no reason you shouldn't get MP1. It's cheaper (usually $6)....and is the first in the series. And arguably a lot better.

But don't worry about which is better...just get off your ass and get the first one....no questions...just do it.

You need it to understand a little about the phazon, thats all...

Thats right, i didnt like the ammo system in MP2.

All you need is 1.

You don't HAVE to, no. But you really should play them both.

get 1
and those questions spoil the game for u :P
"some one" already spoiled it :P

Well both are very good games..
If you liked the Metroid series it is a must have