Can't boot AmigaOS

[Ben Bogart - FMPM/F1999 <bbogart%acs.ryerson.ca@localhost>]

I've run into a situation where i cannot boot AmigaOS.
How can I:

1. Boot netbsd into single user mode without loadbsd, or AmigaOS
2. Change the bootblock so that netbsd will always boot only 
recongnizing the first 4MB of fastram on the motherboard. 
(As I am having problems with my upper 12MB)
3. How can I change the bootblock so that netbsd boots with all 16 when I 
find the problem to my RAM troubles?

Thank you for your time.

Ben Bogart
NetBSD 1.4.1, CUSTOM Kernel, Amiga 3000, 16MB Ram, 2.1GB HD, EGS Spectrum Card.

"CPU clock speed is nothing--system architecture is everything."
 - John Blommers, Hewlett-Packard