i have a window vista ultimate x64 with a flashed motherboard(Gigabyte Motherboard Model:EP45-UD3R). if i upgrade to windows 7, do i have to flash the BIOS again?
You'll need a new SLIC 2.1 BIOS. You currently have a SLIC 2.0 BIOS, which is valid for Windows Vista only.
You can install windows 7 then flash or flash then install win7. Whichever order you like just remember that you mush flash your bios before activating win7 with the certificate and the OEM SLP key dude.