here's an idea - to have the curtain 'slide-able' (is that even a word?)
Anyways, hang a rod curtain holder
http://www.amazon.com/COUNTRY-CURTAI.../dp/B0002AKPH6
the above is a similar concept to what I'm trying to explain
And then at the UPPER slant side, hang a cup holder hook - a small one - and hook the pp aforementioned clip on curtain holders to it - just the farthest left one. That way, even though the curtain is slanted, it won't open on you til you move that one hook that's secured. It would be easier to open/close the curtain - w/o having the curtain always closed - would give you options when hanging laundry/putting away multiple things, etc.
hth.
I live in an old house, too. One gets creative.

BettyAnn
PS If you're really financially strapped - check out the single packages of flat fold sheets - they have all sorts of styles/prints/sizes - and at Walmart - they're under $5 a piece. I use them in a couple of places in my house (one is my pantry area) and NOONE has ever realized they started out life as a bed sheet. Many times, you don't need to do any hemming/sewing at all - just carefully open the widest folded seam just enough to slide a curtain rod in.