Engine Coolant boils--overflows from tank 1996 Caprice?

I've notice my check engine light come on, and off regularly since the beginning of this year. I've also caught some resistance when steering my car yesterday but only temporarily. I get to the store parking Lot and noticed leaking from the battery which was a result from the overflowing, steaming, boiling from the Coolant tank. Any diagnoses? I start classes in approximately two days...