OK, I will tell you what I told EvilLeprechaun:

Go into rmxp, and import them into the Character folder (click the icon to the right of the database icon, or press F10), it will ask you to set the transparent colour, choose the background of the sprites (e.g if the colour behind the sprites is green, then LEFT click somewhere on the green). Leave the translucent colour blank. Press the clear button next to it if you want to make sure it is blank. Your sprites should then work. All you need to do is choose them for your characters in the database. Make sure when you have set them as the characters in the databse, you press APPLY. That might be why it keeps on reverting back to the originals. If you cannot see the apply button then hide your start bar.