> Then I used dd utility to write image on floppies(from another NetBSD 1.5.1
> workstation):
>
> dd if=/dev/fd0a of=./boot1.fs

if means INFILE of means OUTFILE. You've read the blocks of your freshly 
formatted floppy (fd0a) and wrote them into boot1.fs.

> When I try to boot my computer with them(ancient 486) it's telling me it's
> not a boot disk.
> Am I doing anything wrong? Isn't it a right way to do boot floppies?

It is no bootdisk ;) it's only a fresh formatted disk. Only thing you were 
doing wrong is the if / of part

> And one more thing that I don't understand. After writing boot disk with dd
> utility
> md5 checksum changes on original image file I wrote from (on both boot1.fs
> and boot2.fs) . Can someone explain to me why it changes?

As you've copied the formatted floppies into those two files, what else do 
you expect ? ;)

> Please, send replies to my adress mertis@ameritech.net ,

Here we go, fetch yourself a new pair of boot1.fs, boot2.fs files and then do
dd if=./boot1.fs of=/dev/fd0a and your disks will be fine. Have fun with 
1.5.1 ;)

Martin Weber