yummy! CHAFING! A runner's dream come true!
Vaseline, like what SMF said. Or a product called Bodyglide. Or Talcum Powder. Also, make sure to have the clothes that breathe while running...microfiber is it? Bandaids...or here's a weird one...tape. And if you have a hairy chest, might want to uhm...shave it a wee bit. The hairs can cause abrasions.

I am only in 15 minutes of run time, so I am not quite to the point of pain yet...but it is a part I dread so I look up all the itty bitty tips. Hope it gets better for you.