Jaime;
You will need the key that goes with the CD you are using.
Repair Installation: http://www.dougknox.com/xp/tips/xp_repair_install.htm
Windows Updates will need to be reinstalled.
Data should be safe, back-up important data just in case.
Install Service Pack first and by itself.
Then install ALL Critical Updates no more than 4 at a time,
Disconnect the network/modem cable before starting repair and do NOT
reconnect the cable until repair is completed and firewall is
installed/enabled. http://support.microsoft.com/?kbid=283673
