Question about a proposed office network.... All Windows XP systems

Network 1:
Cable Modem ---> Router / Firewall ---> 3Com Hub ---> NIC #1 In
Machine (TCP/IP & DHCP)

Network 2:
3Com Switch ---> NIC #2 In Machine (IPX/SPX & Set IP Address)

I was told running a different protocol such as IPX/SPX on the second
network would make it more secure, is this true?

I understand that the PC's still are connected to the internet on
network 1 but wouldn't it be more secure since network 2 isn't
directly connected to the internet and in order to access network 2 a
hacker would have to go through the firewall and then though the

The server will be on network 2 and will not need internet access.
One would think that since it is on a separate network it would be
more secure than being connected directly to network #1

Any ideas?