OpenBSD 2.3 and 2.5 run fine on this machine. 2.4 works but the pc-card support is broken. You can get 2.4 to work with the 2.5 pc-card support by replacing these files with the 2.5 versions:
dev/ic/i82365reg.h dev/ic/i82365var.h dev/isa/i82365_isa.c dev/isa/i82365_isasubr.c (change irq list here) dev/isa/i82365_isavar.h
I had a lot of trouble with using Partition Magic to resize the Win98 partition. After the resize Win98 wouldn't boot, complaining about missing himem.sys, even though everything was fine with the disk. This looked like some kind of disk cache problem to me so I cycled power and it worked. So I recommend you cycle power (hold the power switch down for at least four seconds) before and after booting Win98.
I have not yet been able to use the serial ports. I think that's because the latest release of Win98 moved them to some obscure port/irqs.
apm does not work. The kernel fails to configure it. See Play with vaio505 for a possible solution which I haven't tried yet.
You have to run XF86 3.3.3 or later because of the Neomagic chip set. This is standard with OpenBSD 2.5. You can get it for earlier versions from The XFree86 Project.
Jim Rees