Pretty much anywhere on the skid plate. There is nothing under there that will be harmed by a common floor jack. You should try to get it under a frame tube though. I dont recomend jacking on the a-arms though.
A good investment if you do alot of work on your ATv is a ATV/Motorcycle jack. I got one last year for X-mas and have used it many times throughout the year.
If not then use a 2x4 and a regular hydrulic jack and jack under the differentals if all your after is to remove the tires.
Guess what Leadtoo (my brother) got me for Christmas? Yep, ATV jack...awesome! It really is stable and lifts the machine up evenly. In addition, you can move the bike around the gargage easily without starting it up and pulling out then back in. Well worth the investment, or better yet, a great gift!
Don't know what stores you have in Alabama, but up here in Illinois, we have a rural supply store called Farm & Fleet. They have them regularly for $69 and quite often with a $20 rebate.