This is the chain of execution:
BIOS -> GRUB -> Windows Bootloader (if you choose it in the GRUB menu)
So if you start up your computer and try hitting F8, those keystrokes will first go to the BIOS, then to GRUB. GRUB doesn't know what to do with an F8 keystroke.
Unfortunately I don't dual-boot, so I'll have to refer you to Google for details on "Windows safe mode with GRUB".
im dual booting win xp/kubuntu.
when i tried to get into safe mose by tapping f8 it wont let me it boots into linux.