Hi Rose,
Your post caught my eye because I created my first academic poster for a conference last year and really enjoyed the process and results.
My advice:
1. Use Adobe InDesign--- this will make your life much easier, and could teach you a new skill in the process. With minimal working knowledge of Photoshop, I was able to create a fairly complicated layout in InDesign. On the other hand, if you are truly technologically-challenged, I've heard that Microsoft PowerPoint is a good way to get the job done.
2. Use as many pretty images as possible-- seriously. People at these conferences will only stop and look at your poster if it is ridiculously image heavy. Think of it as eye candy!
Presenting a poster is not as impressive as presenting a paper, but it is a good way to ease yourself into conference participation. Also, if you can actually get people to stop at look, it is a great, low-key way to network. It does help fill out a CV.
In fact, my poster ended up helping me land two very competitive internships. I gave my interviewers 11 x 17" color copies of the poster as a "take-away." I know it helped, because they each let me know how much they liked it when they called to offer me the spot!
Good luck!