I've just started playing on Party Poker a couple of days ago and over the past couple hundred hands I've run into this problem quite a few times. I raise PF from the blinds or EP w/ a high PP, then bet out my usual bet of just less then the pot, a player that always calls pot bets w/ anything (2 overs, flush draw, open draw, middle pair, middle PP) calls behind me, then the turn brings a scare card (3rd flush card or an A when I have QQ). These players will call a PF raise w/ pretty much anything, especially if they had limped PF and I raised from the blinds. I've even been increasing my PF raises more than normal but these guys call anything. I'm clueless as to what these players have and if that scare card has hit them. All I know is if I check it to them they're betting at me. The couple times I've called them down just to find that the scare card hit them, but these are the same guys who I've seen bet into a PF raiser showing weakness w/ only a low PP and 3 overs on the board. What is the proper play in a situation like this? Do I just give it up and fold or invest more money trying to find out just where I'm at?

Well playing pretty much any mediocre hand out of position sucks, and high PPs are no exception...

Sounds to me like you've just had a bit of bad luck, and are letting it get to you.

If "they" really will bet the turn with anything when checked to, you are correct to call them down occasionally (what's their typical behaviour on the river?), and shouldn't worry about it if you lose.

A few possible variation plays:
(i) If the villains bet the flop when checked to, then check raise the flop occasionally. If they check behind, then bet the turn (almost whatever falls).
(ii) overbet the pot on the flop.
(iii) lead 1/2 pot on flop and turn (almost whatever falls).