Attaching non-load bearing walls to steel I-beams
You have a few options.
Frame around the beam.
This is probably the easiest method, though it changes the dimensions of the room slightly. Simply build your wall either in front of, or behind the beam. Attach the top plate to the joists.
Weld studs to the beam
You could weld threaded, or non-threaded rods (studs) to the bottom of the beam. Then drill holes in the top plate to align with the rods (studs). If you used threaded rods, use a washer and nut to attach the top plate.
Nuts and Bolts
Drill holes through the top plate and the beam flange, then use nuts and bolts to attach the top plate.
Powder actuated fasteners
You could use powder-actuated fasteners to attach the top plate to the beam.

WARNING: For any method that alters the beam in any way, consult an engineer for fastener schedule, size, and placement.