Yes as long as it is a ide hdd ide has the pins the other is sata with no pins so u need to look at yours unless u plan to use it on a external drive then yes it will work on any computer with a external case
You can buy a external hard drive enclosure for a ide hdd. the u just plug this into that and your away a enclosure u can get on ebay for a few pounds or any good computer shop
that's no problem i can put which ever windows u like on there xp vista win 7 win 8 yes win 8 however check your system will run win 7/8 first xp still rules and still the best in my opinion