If you just want to focus then you can use Focus Assist which is designed to be used with the 400D
http://www.xmission.com/~jstanley/focusassist/ . I downloaded a magnifying application as well to help. Zoom into the stars about 6X helps greatly in deciding if focus is close enough.
http://www.freewarefiles.com/program_3_39_13460.html
It works a treat together. A friend of mine had the same problem, wanting to use DSLR Focus. This way is almost as good but you don't get the number of graphs you do with DSLR Focus