sawmill,
We'll need to know more about your I-beam (S for standard beam geometry) before anyone can help you. The I-beam will have a weight per lineal foot as a function of the web thickness and flange width, .ie. 4x9.5 is a 4" standard I-beam with the web @ .326" thick and the flange @ 2.796" wide and will weigh 9.5 lbs per lineal foot. If you do not know the weight you can simply measure the web thickness, look in any steel supliers handbook and get the weight.
Once this is done you need to know the distance between the supported points, i.e. where is it being held up. This, I expect will be supported from beneath at two points on the beam, if not then the beam is you least probelm as now the support connection will have to be calculated.
We'll also need to know if the load is centered or evenly distributed over the length of the beam etc. If your not sure we can use the point load formula and it will be the worse case scenario.
swaneg