All depends on the species of pike. The lugubris pikes get too large for a 75g, but some of the saxatilis and dwarf pikes stay small enough to have a pair or even group in a 75g. If you check the stickies at the top of the pike forum, there should be information about species there for you.
Actually, I just checked and there's not any care or size references... But look through the ID thread and find one you like, and we can probably give you size and care information. Or you can google Crenicichla saxatilis for info. Or dwarf pike cichlid, etc.
i was also thinking of having a pike tank. i have a 180 gal, so any info or suggestions would be appreciated. (beginning stages of transforming the tank for them)