Usually you use a shader tiles the textures by simply modifying the uv information before reading the color from the texture.
For example: If you want to repeat the texture 5 times you have to multiply the texture coordinates by 5 within the shader (and set AddressU and V to Wrap).

However, there are enough terrain shaderes out there.
Have a look at the multi-texture terrain shader in the latest AUM.
It looks pretty good.