Bike sizing...long arms?

I'm a newbie-- training for my first sprint tri. I can't afford a new road bike right now, so I'm looking to buy a used one-- I know fit is the most important thing... I'm 5'9" with a 34 in inseam and long arms--- can anyone recommend a size range I should be looking for? Do I need to limit myself to looking at women's bikes, or could a men's bike be sufficient for a rookie like me for the time being? I don't need the best bike, I just need something to train on that is a little faster than the borrowed mountain bike I'm using right now :>)
Thanks!!

Fit is obviously the most important consideration in a bike. The thing is that many brands have huge sizing differences. My suggestion would be to go to your local bike shop and take a look at the different popular brands and components. See if they can do some quick sizing and give you some suggestions. There's no shame in telling them you might need to look used. Just let them know that they will get your business for repairs and other necessities. They might even know of a decent bike for sale. That will give you an idea of what you are looking at when you jump into the used market.
I am 5'7 1/2" and ride a 54 Specialized Roubaix pro with a shortened stem. I am long in the torso and measured 53.3. I felt better on a 54 than 52 with longer stem. The cool thing with your size you don't need to limit yourself to women's specific bikes. Let us know what you find. The folks on this site are the best for bike advise.

With your measurements, I doubt that a WSD would work for you. I am 5' 5" with a 30" inseam but long arms/torso. I tried the WSDs for sizing and they flat out did not work because of my longer arms and torso. I am riding a 54 Trek 5200. By all means go down to your LBS and try out different sizes and compare WSDs to men's. Good luck!

If you're going to be using aero bars, then your long arms may not make much of a difference compared to your torso length and your flexibility. For a road bike, for example, you might want a longer reach because of your long limbs than you would on a tri bike. With your inseam, you probably want to look in the 54-56cm range. WSD may or may not feel comfortable to you. If you aren't getting a tri/TT specific frame, then a WSD bike could let you get a shorter reach to your aero bars without a huge amount of saddle to bar drop and without putting on a tiny stem. That may not feel so comfortable riding around otherwise. It depends on how you primarily want to use the bike. You might be able make some minor changes to a comfortable road bike fit to make it a decent setup for an aero position. Of course, you don't even have to start out thinking about aero bars at all, but if you think you'll get serious about triathlon, then they are a great way to shave off some time.

I'm bringing this up because I have a pretty long reach on my road bike. I cannot make it a decent setup for use in a TT without changing several parts and making my arms stick out too far in front of me and making me unstable. That's ok, because I don't do a bunch of TTs, and if I do in the future, I'll get a TT bike that is a different size and build. If I wanted to do tris primarily instead of road racing, then I'd be kind of out of luck with the bike I have.

+1 on trying both men's and women's. I'd scarcely even tried women's bikes as i have unusually long arms and all at the bike shops agreed w me. But . . . on a recent Womantours trip I rented a Terry and found it to be amazingly comfortable so I'd rethink that for a future bike purchase.

56 cm mens would probably suit you nicely. :D The womens bikes have a pretty short top tube, i.e. not conducive to longer arms. If you are buying a new bike ask the shop to swap out some parts to fit you better, like narrower handlebars, maybe a different stem or saddle. If you are gonna plop down a chunk o' change they can work with you. :) Don't be afraid to ask. Get it from a shop that is flexible on what they are willing to do. ;)