Lost admin password?

Hi everyone. my name is norrie. ok i will let you know my frustrating problem. I have great computing skill and have never in my life been stuck with any problem computer related. i have always used XP and would class myself as a real xp tech geek. ok so my girlfriends dad decides to give me Her HP compaq 6715b with VISTA business OEM (laptop) and boy I struggle to get to grips with the security on it.

Problem - OK so my login is username workgroup/admin
password "no password"

so i dont have a password which it lets me log into vista ok but when i try to install or really do anything it is asking me for a password

ok so i have all the details like when the laptop was bought so on and product key info but no password. how can i default this ? can i default this?

is there a dirct microsoft technical support number so maybe i could ask them?

or do i change setting in bios?

oh man i am loosing sleep and hair over this i will be soooooo soooooo greatful if someone could give me any kind of help to overcome this.

1. You dont change things in the operating system with the BIOS they are completely seperate (except that they work together in terms of hardware to kernel operations).

You can diable UAC in a multiple number of ways: How to Disable the User Account Control(UAC) in Windows Vista | AskStudent