So, when I configure the HPNA card I should use 255.255.254.0?

Not a networking guru, but to my understanding - no.

Let's say you're using 192.168.0.x adresses for your ethernet stuff, with a netmask of 255.255.255.0 (allows you to have 254 machines/interfaces, 192.168.0.1 through 192.168.0.254, 0 and 255 being used for sort of administrative stuff)

On your HPNA you could then use 192.168.1.x adresses, also with 255.255.255.0 netmask, giving you use of the adresses 192.168.1.1 through 192.168.1.254 for the HPNA stuff

/Michael