Melody to convert high poly onto low poly normal maps...but I found it crashed for me. Silo 2 has a built in normal mapping thing (though you do need to pay for it, unless you download the beta which will last 30 days, but the good thing there is when you update the beta install with an updated one, it'll reset the time back to 30 days, so you can keep on trying it until 30 days after official release.)
For making normal maps from textures, there's this fantastic tool called Crazy Bump. It even lets you edit the normal map in terms of detail and strength. (Can also do displacement and shadow maps)
http://www.crazybump.com/
Just an image from my desktop converted into a normal map.
http://i5.photobucket.com/albums/y173/seppuku05/crazybump.jpg
Hakuna Matata