the shower screen I am getting is for a shower over bath, so its only essentially a pane of glass, 1450m high x 900 w x 10mm thick. Its in 2 pieces, a 1450 x 550mm fixed pane, and a 350 x 1450 pane thats on hinges. According to my calcs the fixed pane is arouns 20 - 25kg of glass. So although its heavy, I think between me and my partner, we will be able to hold it in place to mark out the screw positions.
I am used to carrying around heavy fish tanks a few years ago, and I even built my own 90 x 60 x 60 fish tank using 10mm glass. So I am aware of how heavy it can be (the fish tank above was 70kg of glass alone)
Ben