Adding additional network protocol

I'm interested in adding another network protocol (besides IP) so that I can
connect computers on my home LAN when one of them is running VPN software.
Let's assume two computers on the LAN: one a desktop, the other a laptop.
Before updating the laptop to Vista, both were running Win XP Pro. When the
laptop was running VPN software (Nortel Contivity) to connect to my company's
network, I was not able to connect to my desktop PC, presumably because the
VPN was "capturing" the IP traffic and sending it through the VPN. Therefore,
I added NetWare IPX/SPX protocol to both PCs, which the VPN doesn't capture,
and therefore I could access both resources (i.e. the company network via
VPN, and my desktop PC via IPX/SPX).

After upgrading my desktop to Vista Ultimate (the laptop hasn't changed),
this no longer works. That is, the laptop can access the desktop as long as
it's not running the VPN software; otherwise, I can only access the company's
network. To solve this, I thought I would be able to into the desktop's
network connection properties and add the SPX/IPX protocol just like I did
under Win XP, but it doesn't list any additional protocols that I can install.

So my question is this: Is there someplace I can get the IPX/SPX protocol to
install it on Vista? Or is there a better/alternative protocol or solution I
can install on either/both of these computers that would allow me to connect
the laptop to my desktop while it's running VPN? For example, I thought maybe
I could connect the laptop to my home network using BOTH wireless and wired,
and then directly the VPN software to only capture IP traffic for one of
those connections. But alas, even if that would have worked, there's no
option in the VPN software for capturing IP traffic only for selected
connections.

I would greatly appreciate any help anyone has to offer that may solve this
problem. Thank you grealy in advance.

Joey