how to create TAP device?

I'm trying to use openvpn-2.0 on pmax.
After installed 'netbsd-tap' from pkgsrc,
I created /dev/tapN via MAKEDEV.
Below is vpn.conf
-- cut here --
client
dev tap
proto udp
remote x.x.x.x
port 1194
resolv-retry infinite
nobind
persist-key
persist-tun
ca ca.crt
comp-lzo
verb 3
auth-user-pass
-- cut here --

I got:
"Sorry but you cannot use --dev tap and --ifconfig together on this OS
because I have not yet been programmed to understand the appropriate
ifconfig syntax to use for TAP-style devices on this OS.  Your best
alternative is to use an --up script and do the ifconfig command
manually."

While 'ifconfig tap0 create' gives:

ifconfig: SIOCIFCREATE: Invalid argument

I wonder if there is something wrong with ifconfig or what I need is
just a reboot?

--
sonnie