"Till what size of physical memory do you create swap partition that's twice as big as the physical memory ?" about 32mb..
no seriously, that principle is utter junk these days, forget about it. with a gig of ram, you're unlikely to ever need swap unless you're intending to get VERy hammered.... may as well have around 5oomb if you want to be safe, but i'd doubt you'd even need that really.