damn it, I had to boot form disc due to viruses so my windows is activated to my sister and I used her disc to install windows because the repair went down with the original...
Listen, what you are doing breaches the EULA and nobody here can condone this in any way. However you are allowed to perform multiple installation of Windows to allow for repair / re-installations etc. but after so many installs, as described above, windows will not activate. When this happens you can call M$ and they will reactivate it for you. Best though not to use your sisters copy and get your own.
that kind of language will get you banned. the EULA is a legal contract that you agree to. if you can't follow it, you either need to accept the possible consequences or not install windows.
@parapapa IF both of these computers are store bought they should have windows license key stickers on them, if thats the case then use your sisters windows disc and just put in your key. *The sticker can usually be found on the back of the case, inside the side panel, or rarely on the bottom.