Is this the restore disk for an Acer Extensa 5420?
No the link you provide is for windows xp. If you had vista this will not work because the key on you COA will be for windows vista and you will not be able to activate it. The best solution is to call Acer customer service where the will send you a dvd of the OS and drivers for free if you can find a nice rep or for like $20 usd. Definitely worth the investment because it will be completely clean of everything that you don’t need.