My advice is to wait until August not just for more outdoor training, but mental prep as well. If you do the one in June you may feel rushed and not prepared mentally or physically. I would hate for you to go into to any race not prepared therefore you have a bad experience and lose the reason you are doing the races (for enjoyment if nothing else) You may also consider volunteering at the June race because races are always looking for people to help and there is lots to learn by just being at a race. Just my two cent, but no matter what you decide enjoy it is a blast.

I recommend to hit the pool. If the swim is the weakest part of your triathlon then swim, swim, swim so you will be comfortable in the water. Like Joe_H1 says you can always coast on your bike or walk. But you don't want to choke in the water. You need to feel comfortable in the water. Swimming is my stronger part of the three events do to my past life on the high school swim team But I am a little nervous about swimming in open water for the first time along with 300 other people. Like you said just do it.

I read this article that I found on active.com about a 21 week training program for preparing for your 1st triathlon. It helped inspire me. Its by Dan Empfield and he has a web site called slowtwitch.com. He states that to feel comfortable in the water the key is practice. Try this link http://www.slowtwitch.com/mainheadings/beginner/training.html.

Hope that helps. I'm doing my 1st tri also in Clarkston, Michigan on August 6th, hope to see you there.

I just finished my first tri in Honolulu Mother's Day. I'm a self taught swimmer. I began in a pool beginning of 2005 then moved home to Hawaii in August so it was into the ocean. Even though I had plenty of time to get used to open water swimming I was not prepared for the crowd and panicked a bit.
I would say wait for August and take every opportunity you can to open water swim and if you can find some buddies to swim ahead and/or around you that would be a plus. You'll also need to practice spotting - looking where your going, finding landmarks, buoys etc.... not as easy in open water with a bunch of people as in a pool with lines!!!Then on race day stay to the edge definitely don't find yourself in the middle as I did.

Which ever way you go have fun. I'm hooked and I'm sure you will be also.
Susan

being this is late in my reply you may not get this at all!

i just did my very first tri last weekend (june 11th) at the ann arboe/pinkney, michigan one. it was very difficult due to hills hills and more hills! and the run was on a very narrow true trail. HOWEVER...there were LOTS of newbies along with me that i met.
my friend was supposed to do it with me but wasn't ready for the swim.

tips: for the swim:

1. stay to the back and or off to one side. if in back, let people get a little ahead so you don't get on their feet. that way you do not get kicked, etc.
2.A MUST: YOU MUST BE ABLE TO LIFT YOUR HEAD UP EVERY 5-6 STROKES (or whenever you feel it necessary) to look ahead of you to be able to see where you are going. practice this in the pool every lap you do. if it's very difficult, start out with 1-2 lifts per lap, then add more as you stregnthen your neck up. IF YOU CANNOT LIFT YOUR HEAD TO SEE WHERE YOU ARE GOING then wait to do a race until you are ready. There is no point in swimming in circles (literally). (this was why my friend backed out).

you can stop and tread water to see where you are going when you feel like it (this is where the wet suit will come in handy as it helps keep you afloat). The race i did had 560 people in it. but there were only 31 in my age group along with the clidesdale men in my "wave". so it wasn't crowded.
a wave after you might pass you, but by then the swimmers will be stretched out and not so crowded. it just depends on how many people per wave.

also consider doing the duathlon. that way you get the experience of doing the event but not having the pressure of the swim. so next race you will get an idea of it. Or volunteer as one person mentioned!

my friend got extremely nervous about the swim and almost backed out of doing any tri in the future. i think she will still consider doing one once she is strong enough to lift her head up. I would hate for you to get discouraged and quit before you have a chance to do one!!!! They are very fun: which is the point of it all!!!!

I was 3rd out of the water in my wave (swam during whole childhood competitively!), 27th i think in my bike (i have a mountain bike! very slow!!! i was like the tortaise! not that a road bike would help that much!) and 24th in my age group in my run! But i had a blast!!!! i was 453rd place in all!

it does not matter what you have, just go out and do it!! and have fun fun fun!!
EVERYONE was sooo helpful! i asked many questions to people around me. they were more than helpful and very encouraging!
there are volunteers stationed at points throughout the race cheering you on and giving you encouragement! even the other athletes will encourage you as they pass you, or you pass them!
As one source put it: it's like doing your typical workout with 100's cheering you on!

anyways, i guess i'm babbling here!!!

good luck and have fun!
p.s. my nerves didn't settle until the swim was almost done, and really didn't settle until days later! haha

p.s.s. you can get a surfing style wet suit at costco for $35 or $40. that is what i was going to where, but the water was warm enough. a tri wet suit will help slower swimmers be faster, that is what the owner of the event told me. he said he is a slow swimmer. so it's up to you.