Everyone has given great advice so far. I can understand the fear of telling your friends part since they know you as an advocate for omnivores. I'm the exact opposite; I'm an omnivore that advocates vegetarianism but working on changing the former part.
wink You won't be able to get away without telling them for long if you go out to eat or they make something for you, but you could just simply tell them you're changing your diet for ethical reasons, and they may understand. You can also just ease around it with the suggestions Lorien gave. I like the "I'm just easing off eating meat to see what it's like" kind of reason because, well, it's true. You can also just pull out "I'm just checking to see what this vegetarian hype is all about" and claim that you're just doing research for your omnivorism advocacy. Then pull a CS Lewis and say that doing the research opened your mind and made you decide to change, and why. You might even persuade them to try it out if they see it changed your mind through personal experience.
As for the meat, depending on what meat you have, you might check to see if there is a local wildlife rehabilitation center that would accept a donation of meat. The place I volunteer at is always looking for meat, sometimes even lunch meat or hamburger to feed to the opossums for protein when we're low on minnows. But call ahead first to see what they'll take. You can find a list of links on the National Wildlife Rehabilitation Association's website here:
http://nwrawildlife.org/page.asp?ID=214 or you can PM me your city and state and I can look in my membership directory and give you some contact info. Otherwise, you could keep it around and if you find transitioning from omni to veg "cold turkey" is becoming difficult, you can slowly use it as a transition to becoming veg and wean yourself off. And of course, you can always give it to friends or family that could use it.
But I think I can say from all of us that we're glad you're making a great life choice! You'll find lots of support here and hopefully a lot of information that will keep you on the right track. You can always ask if you need help! Good luck!