after an epic/fraustrating period of 1 and a half days. i finally jailbroke it. turns out that the 4.0 firmware i got from a video is a GM edition which doesnt support jailbreakme.com.
i search this and i search that. after hours and hours. and shitloads of hours. i came to the conclustion that itunes suck. seriously. why the fuck wont you recognise the official and your public release of your own firmware ( probably you signed it steve jobs) Then i change the host file from my windows/symster32/drivers/etc/host file. then i can sucessfully downgrade it to that official firmware of 4.0. what a big waste of time.Turns out its just that damn itunes and firmware that fucked it up. steve jobs is smart. so are we. :) jailbreakme ftw.