Acer Aspire One Netbook for Sale

i already upgrade ram to 512 mb ,also i using with sansung external portible hard disc 120gb.i know my laptop is not standard but it is still useful in very good condition.i love it,and i don’t want to sell him.i wanted to fix him with window vista(business).i would like to know that, can i upgrade him,and if i can upgrade to get good result what i have to change for him. thanks alot.