Well, you can try the LOGON.SCR hack to get in and change the Administrator password. Log in as your user. Then click Start ->Run, type in CMD and click OK to open a Command Prompt.
Type the following:
c:
cd\
cd\windows\system32
mkdir temphack
copy logon.scr temphack\logon.scr
copy cmd.exe temphack\cmd.exe
del logon.scr
rename cmd.exe logon.scr
exit
NOTE: if XP is installed in the WINNT folder, then change C:\WINDOWS\SYSTEM32 to C:\WINNT\SYSTEM32
Ok, after this, log out. Then let the XP box sit for 15 mintues; do not try to log in, or move the mouse or anything. Let the machine sit alone.
After 15 minutes of inactivity, the LOGON.SCR screen saver will be called. Now normally, you would only see a WindowXP picture bouncing around the screen.
Instead, due to the file changing, you will get an open Command Prompt, running with full System rights. This Command Prompt window will have the rights for you to change the admin password.
To change the Administrator password in this Command Prompt box, type in:
NET USER ADMINISTRATOR "password"
hit the Enter key afterwards, and that is it. REplace "password" with whatever password (without the quotation marks) you want the Administrator account to have.
That is it. EXIT out of the Command Prompt window, then log into XP with the Administrator account and the new password! Then you can apply your patches and such.
hope this helps