Non swimmer!

I suppose it depends on what you want to get out of your first race.  My thought is that first race is to try things out.  Knowing how to swim is good enough to finish a sprint tri.  If you're nervous about the open water swim, I'd suggest finding a place to get out and get a sense of how swimming in open water is different from the pool.  Additionally, if your nerves are more about swimming in a large group (something that takes some getting used to, to be sure), then you can always just swim to the side or toward the back of your heat.  I think you'll find that there are plenty of people doing their first triathlons (or even veterans) who aren't particularly strong with their swim, so you won't be the only one not looking like an Olympian.

Dive in, as it were.  But if you have some nerves, see if there are any triathletes in your area who you could meet up with to give you some pointers.  Good luck.

Get a coach for a few lessons.  You'll save yourself a lot of frustration if you learn proper technique from the start.  Even if you don't compete, you'll get valuable technique to enjoy swimming on your own.  Youtube technique videos are great and I watch them too but a coach will be able to see what you're doing and give you immediate feedback....you can't get that from technique videos.