RE4 and RE5 are so different from the other games I don't consider them a part of RE's main story. They both have over the shoulder cameras (like Gears of War), both have thin plots, they have a shop system where you can buy weapons and upgrades, Leon kennedy looks like a girl, Wesker looks like Neo, and there are NO zombies!
I say play RE1 first because RE0 was released 5 years after RE1 and it helps fill in the gaps for the fans. So it doesn't matter if you play it before or after RE1. Its also better to play the first game to come out in the series. That will help you decide if you wanna continue the series.
I would say only buy RE0 and RE1 for the GameCube for now. RE2 and RE3 are really hard to find and expensive.