From my limited experience on DEC 3000/300, netbooting from linux i386:

Firmware 2.3	fails miserably -- arps for 0.0.0.0, tftp bad checksum, timeout
Firmware 3.3	tftp boots first image but fails in prom_open (code 4) for NFS
Firmware 6.3	claimed by various people to work ok
Firmware 6.5	works for me to boot the 1.4 install image
Firmware 6.7	works for me to boot the 1.4 install image
Firmware 7.0	failed for me -- tftp timeout; might try again 
		with netboot.broken if I have time

Note: you can find the current firmware revision number from the SRM console:
>>> show config
Look on the CPU OK ... line, should see Vx.y there.  

Things I did wrong:
	implicitly blocked packets from 0.0.0.0 in my linux firewall
	forgot to power cycle machine after burning prom
	needed ":hd=/tftpboot" in /etc/bootptab

Things that may have helped:

	added ":hn:vm=rfc1048" per http://www.cs.rutgers.edu/~armhold
	shortened bootbtab entry (no gw, ns, lp, etc) so hostname would fit
	in bootp packet
	
Here's my working bootptab entry:
-------------------
.allhost:hd=/tftpboot:\
	:sm=255.255.255.0:\
	:sa=192.168.110.1:\
	:hn:vm=rfc1048:\
	:to=auto:

# All alpha entries -- netboot copied into /tftpboot from /usr/mdec/netboot
.alpha:bf=netboot:rp=/usr/export/alpha:tc=.allhost:
#.alpha:bf=m300_v6_7.btp:tc=.allhost:

# Define all individual entries.
host.my.domain:ht=ether:ha=08002bxxxxxx:ip=192.168.110.4:tc=.alpha:
-------------------

Hope this helps, and perhaps some of this info can make its way into
the netbooting alpha HOWTO someday.

	Dave Johnson
	ddj@world.std.com