window98 cd keys

hi i want to know about windows 98 cd i have installed windows 98 cd in my system i don't have cd key so i got from my friends pc j6ckk-6jv8f........ and it's working i also applied another cd key it's working so i want to know how we know that the cd key of win98 sec is correct and how long it works and what is the best way of windows 98 instaltion usually i bootup from cd rom and install so any adea install windows98 sec edition and how we know that about cd key windows 98 sec for full version
can u explain thanx a lot .
system info.
win98sec
4.10.2222 A
P4 Intel
128mb ram
40 gb hard drive