Hi, I lost my cd for XP, however I still have my key. However I donwloaded a version of xp from internet it don't work on it, also I read that you must have the same version xp to get that cd-key to work. Therefore I wanted to know is there anyway I could check what version my cd-key is for?

Call Microsoft, tell them the key number, and they will tell you what version of Windows XP it's for.

To my knowledge, there's only 2 versions of XP... Home and Pro

I know the key is different from oem home, oem pro, oem corp, retail home, retail pro, but I try all of them and it don't work, I wonder could it be because those I donwloaded is SP2 include, do I have to get the older version

You can always try using the older version, then if it works for installation, update Windows using the Windows Update feature in your Start Menu.

you can also look in the registry to see what existing key is being used (if you know how).