If you are talking about sloping tiles, the math goes something like this:
First, take the change in Y (if your tiles are 32*32, then sloping up toward the right would be -32, while if you're sloping down as you go right, it would be 32), and divide it by the change in X (which would normally be -32, given 32*32 tiles). We'll call that the slope.
Now, with the slope figured, we can adjust the height of the object based on its X position. So, something like this:
object.Y = slope * (object.X - tile_object_is_on.X1) + tile_object_is_on.Y1;
Where "tile_object_is_on.X1" is the left-most point of the tile (i.e. object.X % 32), and "tile_object_is_on.Y1" would be the left-most point's elevation (tile_object_is_on.Y + 32 for an up-to-right slope, or tile_object_is_on.Y - 32 for a down-to-right slope).
Hopefully I explained it well enough (and got all my numbers right -- I'm no math scholar
). If you have any trouble or other questions, let us know!