Well , my timezone is GMT+8 , I live in south east asia , I usually online bout 2/3 PM till 5/6pm but i won't be able to online in a few days[2-3 days] due to OVERWHELMING homework...
actually I use the CS5 too , this just a matter of colour range tool...
you just use colour range Select Tab > Select Colour Range > Select your colour U wish to select[in this case,white], then after selecting it , unlock your layer[if its lock] then press delete , your transparent-no white background appears...
There TONS of stuffs you can do with this colour range tool[is it call a tool anyway?]