how to build an inline ids?

[spy guy <spyguy703 () earthlink net>]

I have a question and I was hoping someone could help.

Is it possible to build an x86 based PC as an in-line IDS?

I want to install Snort IDS at home, but have no taps or equipment that
can mirror/span ports.

Can I build a Linux PC with 2 nics and put it inline between my firewall
and adsl modem?

I would like to have the NIC's in some sort of 'Stealth mode', so that
no IP's are needed and thus my network config will not change. I just
want the NIC's to pass traffic in both directions and then run snort to
monitor the traffic on both.

Is there a way to do this?