Solaris 64-bit to 32-bit

I had previous implemented the following in my menu.lst to be able to get to 32-bit operations.

# 
title Solaris 10 32-bit
root (hd0,0,a)
kernel /platform/i86pc/multiboot kernel/unix
module /platform/i86pc/boot_archive

</code>
Now, it is not working as I get the following error :

Multiboot is no longer used to boot the Solaris Operating System.
The grub entry should be changed to 
kernel$ /platform/i86pc/kernel/$ISADIR/unix
module$ /platform/i86pc/$ISADIR/boot_archive

</code>
Now, if I do echo $ISADIR it is NULL with no output.
I got to do this, b'coz my VIA Rhine III vfe network drivers only work in 32-bit Solaris OS

Regards,
Praveen.