You can download rm2k off more places than rm2k3. Besides, rm2k3 is just a minor update with a new battle system and miscelaneous add-ons. Also note that you need the program and the Run Time Package (RTP). Those are the files (maps tiles, characters, sound effects, music, etc) that you will need to start making a game.
Pokemon games are hard to make with rm2k.I'm thinking of publishing a tutorial on that in the Pokemon Technical Institute here at PC (no one steal that idea though ;) ) You'll want to get some more experience with the program before attempting to tackle pokemon games. The best way to learn is by downloading, playing, and disecting other peoples' games. To download some, try these sites:
www.gaminggroundzero.com
www.gamingw.net
You can also download Pokemon resources from the
www.gamingw.net one. For example, you can download the pokemon graphics, pokemon characters, and all that good stuff. If you need pokemon music, check out
www.vgmusic.com. You can download music from various video games there. If you are musically inclined and want to compose/arrange your own music, download Anvil Studios. You can get it off
www.gamingw.net. If you want to make your own music but you are not familiar with miusic theory, try searching for "Melody Raiser." Point, click, instant catchy tune. Anything else you need to know, you know who to call!