tcp/ip routing question / router design

["first last" <in5ecure24 () hotmail com>]

hello everyone

I have a question bout which way is a better implementation for a router, 
heres my situation.

I have a dsl "modem" that is a router, but it only has 1 ethernet port. im 
saposed to plug the dsl stright into my pc but im not, i have both connected 
via a switch and everything worked instantaly, so im assuming i can plug my 
servers into the switch and run my network.

What i am trying to do is set up a DMZ, and my LAN to the internet. the 
first way i was going to do this was via a software router/multihoned pc (3 
nics 1 for each network) and set up a firewall and routing ect ect, on that 
pc to securly route my networks.

1 problem is if i use only the dsl as a router (isp -> dsl -> switch -> pcs) 
then what do i do about having seperate networks for my LAN and DMZ and 
internet conectivity? on the otherhand...

If i use a pc as a router seperating my DMZ and LAN is very easy since i 
have a nic for each and 1 for my dsl. i dont see why i cant do this but, 
this will consume a pc, and i dont realy have an extra one.

so my main question is which way do i go w/ or is there other good options, 
mind you money funds are low so simply buying a hardware router isnt realy 
an option. My dsl has options for setting up a public and privet lan, but 
its not like i can physicaly distinguish between the two.

So im pretty much just looking for the best way to set this up (from a 
security standpoint) and recomendations, help, feed back is GREATLY 
apricated - thank you

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