Vista - Forgot Admin password for Vista Business

I bought my computer with Vista Business intalled. I've been using the
administrator profile (as my profile) up until yesterday when I switched it
to a "user". I assigned the ASP.NET profile as administrator and did not
assign a password. When I restarted my PC, now there is no way for me to
access the administrator rights since it requires me to input a password. Is
there a default password for this, since I did not assign one in th first
place? Now there is no way for me to change the settings of my PC.

Please help!!!