Just manage to install OpenBSD 4.0 to Blade 100 using diskless method 
Have fun!
# dmesg
console is keyboard/display
Copyright (c) 1982, 1986, 1989, 1991, 1993
The Regents of the University of California. All rights reserved.
Copyright (c) 1995-2006 OpenBSD. All rights reserved. http://www.OpenBSD.org
OpenBSD 4.0 (GENERIC) #953: Sun Sep 17 00:56:22 MDT 2006
deraadt@sparc64.openbsd.org:/usr/src/sys/arch/sparc64/compile/GENERIC
total memory = 268435456
avail memory = 233144320
using 1638 buffers containing 13418496 bytes of memory
bootpath: /pci@1f,0/ide@d,0/disk@0,0
mainbus0 (root): Sun Blade 100 (UltraSPARC-IIe)
cpu0 at mainbus0: SUNW,UltraSPARC-IIe @ 502 MHz, version 0 FPU
cpu0: physical 32K instruction (32 b/l), 16K data (32 b/l), 1024K external (64 b/l)
psycho0 at mainbus0: pci108e,a001, impl 0, version 0, ign 7c0
psycho0: bus range 0-1, PCI bus 0
psycho0: dvma map c0000000-dfffffff, iotdb 1360000-13e0000
pci0 at psycho0
ebus0 at pci0 dev 12 function 0 “Sun PCIO Ebus2 (US III)” rev 0×01
“flashprom” at ebus0 addr 0-fffff not configured
clock1 at ebus0 addr 0-1fff: mk48t59
ebus1 at pci0 dev 7 function 0 “Acer Labs M1533 ISA” rev 0×00
“dma” at ebus1 addr 0-ffff ipl 42 not configured
power0 at ebus1 addr 800-82f ipl 32: can’t map register space
com0 at ebus1 addr 3f8-3ff ipl 43: ns16550a, 16 byte fifo
com1 at ebus1 addr 2e8-2ef ipl 43: ns16550a, 16 byte fifo
“Acer Labs M7101 Power” rev 0×00 at pci0 dev 3 function 0 not configured
ebus2 at pci0 dev 7 function 0 “Acer Labs M1533 ISA” rev 0×00
“dma” at ebus2 addr 0-ffff ipl 42 not configured
power1 at ebus2 addr 800-82f ipl 32: can’t map register space
com2 at ebus2 addr 3f8-3ff ipl 43: ns16550a, 16 byte fifo
com3 at ebus2 addr 2e8-2ef ipl 43: ns16550a, 16 byte fifo
gem0 at pci0 dev 12 function 1 “Sun ERI Ether” rev 0×01: ivec 0×7c6, address 00:03:ba:08:53:1b
ukphy0 at gem0 phy 1: Generic IEEE 802.3u media interface, rev. 1: OUI 0×0010dd, model 0×0002
“Sun FireWire” rev 0×01 at pci0 dev 12 function 2 not configured
ohci0 at pci0 dev 12 function 3 “Sun USB” rev 0×01: ivec 0×7e4, version 1.0, legacy support
usb0 at ohci0: USB revision 1.0
uhub0 at usb0
uhub0: Sun OHCI root hub, rev 1.00/1.00, addr 1
uhub0: 4 ports with 4 removable, self powered
“Acer Labs M7101 Power” rev 0×00 at pci0 dev 3 function 0 not configured
autri0 at pci0 dev 8 function 0 “Acer Labs M5451 Audio” rev 0×01: ivec 0×7e3
ac97: codec id 0×41445348 (Analog Devices AD1881A)
ac97: codec features headphone, Analog Devices Phat Stereo
audio0 at autri0
midi0 at autri0: <4DWAVE MIDI UART>
pciide0 at pci0 dev 13 function 0 “Acer Labs M5229 UDMA IDE” rev 0xc3: DMA, channel 0 configured to native-PCI, channel 1 configured to native-PCI
pciide0: using ivec 0×7cc for native-PCI interrupt
wd0 at pciide0 channel 0 drive 0:
wd0: 16-sector PIO, LBA, 14594MB, 29888820 sectors
atapiscsi0 at pciide0 channel 0 drive 1
scsibus0 at atapiscsi0: 2 targets
cd0 at scsibus0 targ 0 lun 0:
SCSI0 5/cdrom removable
wd0(pciide0:0
: using PIO mode 4, Ultra-DMA mode 2
cd0(pciide0:0:1): using PIO mode 4, Ultra-DMA mode 2
pciide0: channel 1 disabled (no drives)
vgafb0 at pci0 dev 19 function 0 “ATI Rage XL” rev 0×27
wsdisplay0 at vgafb0: console (std, sun emulation)
ppb0 at pci0 dev 5 function 0 “DEC 21152 PCI-PCI” rev 0×03
pci1 at ppb0 bus 1
pcons at mainbus0 not configured
No counter-timer — using %tick at 502MHz as system clock.
uhidev0 at uhub0 port 3 configuration 1 interface 0
uhidev0: Sun Microsystems Type 6 Keyboard, rev 1.00/1.02, addr 2, iclass 3/1
ukbd0 at uhidev0: 8 modifier keys, 6 key codes, layout 33
wskbd0 at ukbd0: console keyboard, using wsdisplay0
uhidev1 at uhub0 port 4 configuration 1 interface 0
uhidev1: Sun Microsystems Type 6 Mouse, rev 1.10/1.05, addr 3, iclass 3/1
ums0 at uhidev1: 3 buttons
wsmouse0 at ums0
root on wd0a
rootdev=0xc00 rrootdev=0×1a00 rawdev=0×1a02