Liamster,
MrChad was telling you how you should install your XP. He was not telling you to buy a full version instead of an upgrade.
As he suggested later, you can use an upgrade version and still do a clean install.
The name "Upgrade" is confusing!
If you have a win98 CD, you can get an XP upgrade and make a clean install of XP without ever needing to install 98 save some money without any loss.