[CentOS] Newby- New install forgot Login - pwd

Hi,

I have just spent a whole day installing Centos 5.3 on an old machine 
and now as I take disc 4 out and reboot, I get the first black screen 
with Login and Password.

I can remember being asked for one Login and pwd early in the install 
but chose not to use one, then it asked what the box is going to be 
called and I said Linux...
(I think).

How in earth can I get myself out of this??

Please!!

oz

:-(