The webserver seems to be having a hard drive issue. Not sure when it will be back up.
I use L3DT to make the heightmaps and textures I use for BT.
BT SetTerrainScale : Scales the terrain on the X and Z axis, giving you control over how much area the terrain covers.
BT SetTerrainYScale : Allows you to set the scale of the height differences in your terrain.
BT SetTerrainSplit : The terrains are split into parts that the culling system uses to improve performance. There are minimums and maximums depending on your heightmap size, and the value of BT SetTerrainScale. You'll have to experiment to find the right setting for your situation on that one.
BT SetTerrainDetailTile : If you supply an image to BT SetTerrainDetail it will use that image across the entire terrain to give a bump map look to it. BT SetTerrainDetailTile allows you to set the scale of that image as it's repeated across the terrain.
Hope that helps.