setting up and testing a linux router on an internal WAN

I have a project that I'm working on to replace 3 dedicated Linksys
WRT54GL routers running the v24 beta of dd-Wrt with a dedicated linux
machine or VM to handle their traffic. This is primarily because of
the 10 slots available for EoIP tunneling (we use this to connect our
satellite sites to our WAN/servers) which we will be expanding beyond
eventually, but also because we expect that within a year or so our
bandwidth will exceed what these routers are able to effectively push
with QoS and everything else.

I've ended up getting a copy of the 'vmwarez.com ipcop basic test rig'
in order to start learning about using the Linux kernel to achieve
packet forwarding. Unfortunately I'm not really sure about a few
things and I'm finding the several documentation sources that I've
checked relatively unclear about these matters:

a) My test machine is a 10.x.x.x. I am attempting to route traffic
from a ubuntu linux laptop through one NIC that the test machine has
dedicated access to over another NIC that the test machine has
dedicated into a 192.168.1.x subnet. Does the test machine have to be
numbered on a different subnet? Also, the laptop is currently
specified as a 192.168.1.x; I won't learn anything about whether the
packet forwarding worked unless I change its subnet, correct?

b) Is this already 'EoIP' tunneling? Or will I have to configure
other packages to work in conjunction with this test machine?

c) how about PPTP (which I'm fairly certain that we use to allow home
workers to VPN in) and/or the openVPN package?

d) Is this testing hardware configuration (ie our WAN<-->routing
machine<-->laptop) suitable for testing a this router machine to be
used in a configuration such as our ending one (ie Internet/our WAN<--
>routing machine<-->homesite LAN)?

I'm also definitely looking for any sources that you could recommend
for showing useful and concise instructions or well presented general
information that would be useful for this setup. There's a huge
amount of documentation on this out there and I'm finding that the
majority of it is rather confusing; some of it is starting to make
sense as I become more familiar with the networking concepts, but up
until now the networking issues around here have been others' jobs and
not my own, I've been strictly protocol configuration, scripting, and
administration.

Thanks for anything you can point me at or any tips you can give, it's
very much appreciated.

Damo