Hi

I don't see why you could do this. If pix v7.x then as you say make it same security level and add command

same-security-traffic permit inter-interface

which will allow traffic to flow freely between interfaces without access-list and NAT.

Be aware though that this is not acting the same as a switch because each interface will need to be in a different vlan/subnet. This may or may not be an issue. if you need the same subnet you could look at using transparent firewall feature but i wouldn't like to say whether that will work or not without testing.

You would need to use cross-over cables to connect pc's into pix interfaces.

HTH

Jon