brand new swimmer

Ok, I have been running for a couple of years and riding for about six months with the intention of doing some tri's this year. I figured that I would put off the swimming for a while, how hard can it be right? Well, I just tried to swim today ( for exercise I mean, I CAN swim ), and it was a very rude awakening. It took me about twenty five minutes to get in 300 yards. My question is meant for other noobs with no swim background or coaches....Is there a rapid progression in this sport once you get some instruction? I have access to a very good masters program which I now intend to join. I know that it takes a long time to master swimming, but can I reach the point to where I can complete an Olympic distance (1500M) swim in 3-4 months with instruction? I was totally shocked at how miserably I performed. Hopefully there will be some good news in the responses. Thanks