I have been wondering the mechanism of default display size
for G2 Macs for a long time.

My impression is that the value is stored on disk. 

Somewhere in one of following etc.

 1: Apple_partition_map Apple                 63 @ 1       
 2:      Apple_Driver43*Macintosh             54 @ 64      
 3:      Apple_Driver43*Macintosh             74 @ 118     
 4:    Apple_Driver_ATA*Macintosh             54 @ 192     
 5:    Apple_Driver_ATA*Macintosh             74 @ 246     
 6:      Apple_FWDriver Macintosh            200 @ 320     
 7:  Apple_Driver_IOKit Macintosh            512 @ 520     
 8:       Apple_Patches Patch Partition      512 @ 1032    

If I wiped out those stuff while installing NetBSD, 
the information is gone.

If you set disaplay size in MacOS 8 or 9, and then 
installing NetBSD in the manner that some info in above
is preserved, the display size stays what you set in Mac OS.

Am I wrong ?
---
Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.