Can you build any chest muscle at all by pushups, I currently dont have access to weight equipment, and wondered, do Pushups really help at all? And also what about other exercises w\o weights, situps or crunches?

The answer to your push-ups question can be found in another post somewhere -- I'll try to link it up.

As for crunches and sit-ups, I think they're effective for most people, although I've seen a lot of people using weights for their ab exercises.

http://forums.johnstonefitness.com/showthread.php?t=379&highlight=pushups