actually my openvpn server has:

push "dhcp-option DNS 65.24.7.3"
push "dhcp-option DNS 65.24.7.6"
(these are Time Warner cable / Road Runner DNS servers)

But on both Windows and Linux clients, it doesn't pick up the setting correctly.
The DHCP request gets "192.168.1.1" back from the openvpn server as a name server, and it seems to work correctly.

As for tap vs tun, I don't remember why I picked one over the other. Maybe I just copy/pasted the config from somewhere... or maybe there was some issue supporting Windows? Anyway, I currently have it working correctly from 3 clients simultaniously:
Ubuntu Linux
Nokia 770
Windows XP