I have recently bought a game and i want to install it onto a computer my room....however someone has disabled my ability to install things onto the computer......

can someone help with this problem and guide me to fix this.....
i think i have to go to the administrator account...but i dont know the password... can someone help me with that too....(to hack into the admin account)...

Its an olda version of XP I think....
Microsoft XP Professiional
Version 2002
Service Pack 2

Thx.... :)