A friend of mine gave me a computer - not bad; 2GHz, enough ram, enough HD space, etc. for what I want to use it for (utility standby, mostly). Unfortunately, it came with XP Home and I'll need XP Pro.

I see on eBay people selling the COA stickers from "decommissioned computers". What exactly does this mean? I have an older PC in the basement running XP Pro that is not strong enough any more - can I "decommission" this computer and re-use the COA? Would that mean if I ever use the old PC on line Microsoft's security police will come knocking?

I have the software and a valid license. I just want to transfer it to another machine. I know it's possible because I went through it before but I've forgotten exactly how I did it.

Any help appreciated.