ok, here is what i did
i followed all steps from this guide here
wiki.remote-exploit.org/index.php/Howto#Live_install.2C_dual_boot_from_grub
but it didn't work

so i looked up another guide here
forums.remote-exploit.org/showthread.php?t=7844&page=14

i run bootinst.bat from the HD that contains BT3 live

But it now set this HD of BT3 live active and i can't boot to my previous OS(i run linuxmint dual with Xp). however i can boot live BT3 from HDD now

i tried to re-active the linuxmint HDD, but it won't boot?
i checked boot/menu.lst of linuxmint, and its still the same.

Anyone know how to fix this?

thank you