i purchased the WD 320gb hard drive for my mbp. before i install it, i wanted to make sure of one thing. rather than reinstall everything via discs, i planned on using my latest time machine backup from my external hard drive. once i finish the install and boot up my computer for the first time, will it prompt me to insert a disc? or copy from another machine? or what? new to this so i want to make sure i do it right. thanks!