when you say a 'flimsy' plaster wall... are you sure you want to hang a screen off of it?
if its just a stud wall, which i assume it would be - you really need to find out where the studs (the timbers) are spaced - they're usually 16" centre tp centre, but they're not always ;o)
once you've confirmed this, you need to be really sure there are no pipes/wires in the wall. the screen you mentioned should weigh in it around 30lb's or there abouts, so a regular bracket from the likes of vogels should be more than good for the job. some hefty (2.5" long) timber screws (i use the 'turbo' range from screwfix) use as many screws as you can too.
hope this helps.