Well, I agree that the pictures would look terrible in a more serious RPG, they are fine for a joke game, which I imagine this is seeing as the game over screen is a picture of Bush and Cheney as Beavis & Butthead. That being said, having floating heads as enemies is rather strange. I would suggest that if you go that route, you should have no battle background and also remove the background of the pictures. What I mean by that is simply isolate the heads and get rid of the landscape/setting that can be seen behind them.
But yeah, every RPG is different (well, a little bit at least), and so if you do choose to use floating heads as enemies it is fine. The only thing I'd suggest is that you remain consistent in your use of graphical elements. Don't make some of your enemies floating heads while the rest are RTP or anything - make them all floating heads.
Also, you don't need to double post. There should be an icon next to the post that says modify. You can use that to edit your original post.
And yeah, as Irock said, you can post 'adult' sprites if you so choose. Maybe put them in a spoiler labelled NSFW in case a kid accidentally wanders into RMRK.
Also, Paint is fine unless you want to do serious editing. If you want a free alternative to Photoshop, then
Paint.NET is fairly good, even though it really isn't close to being as good as Photoshop. For a list of other free programs, check out this thread:
http://rmrk.net/index.php/topic,11188.25.html