Installing FreeBSD 5.1 - Boot manager doesnt install itself

[y.patil at attbi.com]

I have two disks on my machine - the first has WinNT while the second had linux. I used Lilo 
to select which OS I wanted to boot. 

Replacing linux, I installed FreeBSD 5.1-RELEASE on the second disk. In spite of selecting 
the Boot manager for installation, it still doesn't seem to install itself. I still see the Lilo menu at 
boot time. 

When selecting the boot manager option during installation, I am asked on which disk the 
operation should be performed on, and it selects ad1 (the second disk) by default. Using ad1 
as the default suggested choice results in no boot manager prompt after install completes. If I 
select ad0 instead, I get an error message saying "only one fat allowed as a child of whole". 

Whats the problem here? Thanks in advance

Yatin