Hi,
In SRM console >>> show boot* will list environmental variables, set
command can be used to unset bootdef_dev variable which is trying to
boot linux. Do at SRM  prompt >>> set  bootdef_dev , set boot_osflags ,
this on next boot will allow you to >>>boot dva0 , to start install. On
the as800 there is a jumper on the mother board (J27) moving it  over to
ground pin will allow you to use other vga cards or a tga video card.
The S3 TRIO64 embedded chip , is supported for install in netbsd, but is
not supported by X- XalphaNetBSD  (no X with this vga video chip). This
option (J27) allows you to install a pci, PBXGB-AA card which will be
recognized as a tga2 card in netbsd, and XalphaNetBSD sever will support
this card -X will run  and has worked well for me. Alternatively, work
is continuing on XF86-4.0.3  support for netbsd on alpha, where your S3
Trio64 chip may have support.
-Mel