how 2 change ms office xp 2003 pro cd key?

[bournurplusher]

my os xp sp2.i have office xp 2000 premium version.its a geniune one.but i cant able 2 update my office xp.if i go 2 office update,its needed 2 install sr1-a update.but i cant install sr1-a update .its asks office 2000 cd.i dont have office 2000 original cd.so i can download 3rd party office xp 2000 premium.i can use that cd,2 install sr1-a update.but still i cant update.
so i can decided to install newer version office xp.i can install ms office xp 2003 pro 3rd party bundle.now i can use office xp 2003 pro bundle.but i cant able 2 update,coz, valitation failed.so i can decided 2 change my office xp 2003 pro key.
i can download win key finder1.73 rc2 & install in my system.i can try 2 find my current office xp cd key,using win key finder1.73 rc2.its shows my current key.i can delette my current key,then paste new key.but my prob lem is,i can able 2 change my cd key only once.that key failedin validation test.so i can try 2 change another key.but i cant change.why this happend?win key finder1.73 rc2 changes keys in only once?
if i click change key button,autometically open ms word.i dont know what can i do next?anybody knows how 2 change office xp 2003 pro key?plz explain step by step