A question about creating a transparent(IP spoofing) WWW proxy /gateway

Hi,

I have a following question. But I'm not sure about the right newsgroup
to ask it. I posted this to two NGs and set the followups to the Windows
NG. If neither is the right place, please direct me to correct one. Yes,
I know this is a tricky question.

I have two computers. Primary runs on Win2000 Pro and has a fast
connection. Secondary runs on Win95 and has a slow connection. The
secondary offers some services, like WWW. For the record the WWW server
is Apache 2.0.47. So normally people connect to the secondary computer,
ask for data and it replies with it directly. But I want to set up a
truely transparent WWW proxy on the primary computer which the secondary
takes advantage of. So that instead of the previous, people connect to
secondary computer, request data, and instead of sending the data
directly, it forwards the data to primary computer proxy server, which
then sends the data to the target computer, faking it's IP to be coming
from the secondary computer. I hope you got the picture. Is this
possible to do with Windows software? If not, then is it possible with
some Linux software? Also, is the IP spoofing necessarily? I think it
is, but if the target computer would accept the data from another IP,
then there is no need to fool it.

I have have a feeling, and this system would mean my primary computer is
a WWW gateway to the secondary, is this true?