Onk...one of the reasons I don't even make tiles,,,is when you apply them you see the icon more than the tile. They look ok I guess but it's just not worth the trouble to make them.
And if you have PS....open the dock bg your trying to fix...and using your elliptical tool at the top left of the tools...just cut out the middle and then move to 2 sides together...and sometimes it works out ok as a tile.
Then go to the dock background gallery and find a tile and snatch the .ini file out of it...then all you should have to do is tweak it a bit to your liking.