Harddrive Some Questions, lock/unlock, put hdd back in pc again Options

[Kojak]

I´m planning to put in my seagate barracuda IV 40Gb temporary until i buy a bigger one. So i have some questions, after i bought a new bigger hdd, can i use my old seagate without any problems on my pc again, or will the zeroing be a problem?? I´ve head som talk about lock and unlock hdd, and i don´t understand it, i´ve got an 1.1 box and isn´t it just to follow an guide and put it in?? Or what is the problem with lock unlock on 1.1 and why should i even lock/unlock??