I was directed to this site by an engineering forum when I made a query about a deflection calculator for steel beams.
http://www.geocities.com/richgetze/
I downloaded the freeware and it works quite well. It requires some knowledge of loads types and values.
I would suggest that you download it from the guy's homepage but he has some bandwidth restrictions hosting it on Geocities. I uploaded a copy to my server if anyone has trouble getting a copy
http://www.buildersmatrix.com/info/beamb22.zip