Accessing the administrator account?

Hi,

I just did a full reinstall of my Windows XP Pro using the disks provided by
the manufacturer, HP. During the install it made me create a user name,
personally I don't want to use this user name I want to use the
administrator account. I can see the account in Manage Computer but I can't
figure out how to log into it. Eventually I will attach this computer to a
domain and they I'll primarily use the domain admin account but in the mean
time I'd like access to the local administrator account.

How do I do this? I don't recall having this trouble in the past, in fact I
rebuilt this same system last week and did not have this trouble, it didn't
even prompt me to enter a user name. Any suggestions?

Thanks in advance,
Linn