Haven't played the old gameboy games in a while, but can't you see what area of the map Entei and Raikou are currently in? I'm currently playing through SoulSilver and I ineptly knew to run back and forth between two routes/town until one of them was close so I'm guessing I did that back in the Crystal days but now that I think about it maybe I got that idea from the roaming Pokemon in Diamond/Pearl.
Yeah, but in Crystal, you don't get to encounter them first like you do with Mesprit, Cresselia, and some other roamers. You have to randomly find them first, which is a pain.
I remember seeing Entei once on my Crystal version when I was younger. It fled from me, so I shut off the game, thinking I'd have another chance. Sadly, I never saw it again...
Official Chespin of the Pokemon X boards. http://www.youtube.com/Decon082/