Yes, I know that question you're talking about, and it will not appear again on your PC in the admin account unless you completely wipe itunes including registry entires. I am not sure about the other accounts.
iTunes installs in all accounts. It will already be there in the other 4 when you check at home.
You're smart to use different windows user accounts. That way everyone can have their own ratings & play counts. Method 1 from this article
http://support.apple.com/kb/ht1495
Make sure to click on the link about sharing music between different accounts on the same PC.
Put the music & videos in a shared folder. Make sure everyone's itunes has advanced preferences turned off to copy music. This will prevent your hard drive from filling up with duplicates.
You might want to look into using 'itunes folder watch' to keep everyone's library updated with new music. Just google for that little program.