Personally I wouldn't discount Wilbur as its real good and would get you a long way with what you need. All of the apps usually need a starting point tho and thats what making your own contours can help with.

I'll describe it again tho. You start off with a 2D sketch or rough map of what you want. You make it greyscale and then what I like to do is set it so that the darkest point on the map is mid grey going up to white - just so that I can see what it looked like before. Then take a black pen a few pixels wide and draw in all of the countours so you end up with a 2D image of wibbly lines. Make sure they join up correctly or go right to the edge of the image.

Next, use the contrast tool to whack it right up so that its just black contour lines and white background and no shades of grey. Then use the flood fill to fill in every alternate contour region. So you should end up with a set of zebra stripes. The more stripes you have the better.

Now when thats done, figure out how many stripes you have counting from the lowest altitude on the map to the highest. Divide 255 into that many and lets say you had 16 stripes so thats shades of grey of 16 each. Start at the lowest stripe and keep it black, take the next white one and flood fill it with grey shade 16, take the next black one and flood fill it 32 take the next white one fill it 48 etc all the way up.

Now you have a height map which is all shaded but banded in quantized values of 16. Use a large blur to smooth out the bands. The more bands you made the easier this process will be. You can add the noise at this point.

Like Waldronate says, its a good idea to start somewhat small like 1024 sized image and then add a bit of noise, blur it, then scale up by a factor of 2 then add some more noise then blur it some more then scale up by 2 again till you have a suitable sized bitmap.

Once you have it at that state then you can push it through Wilbur or other apps to refine it and add better water courses etc. It gets a lot harder from this point to make it look truly realistic but that is the challenge. At this point you can multiply in some real NASA mountains and lowlands to make it look a little more realistic. Nobody has a perfect solution to getting this last bit right but some apps like World Machine do a fair job at it.

If at any point you want to see your height map in 3D you can use my little free app:
http://www.viewing.ltd.uk/cgi-bin/vi...dragons_flight

Save the height map as Height.bmp, put the app in the same folder and run it. It will complain you dont have a colour.bmp either but ignore that one. If you used a 1024x1024 bitmap then press '6', if you used 512x512 then press '4' and the keys to move around are shown in the initial help dialog.

If you use Global Mapper then you can add in GIS style vector contours and get it to generate the 3D height map from them. You can then export it. The advantage there is that you can go back in and add more of them and edit them. In MeDEM we use Global Mapper style.