Building a linux multi port router

[bajangerry]

Hi,
I am considering building a multi port router using Linux and would like some advice regarding how I could best achieve this. What I essential want to do is to provide a means of routing traffic between 4 existing networks in a building to provide a common point of Internet access. The networks should(but not essential) remain separate from each other as in not routing between them but be able to access the internet via a single network adapter in the Linux box. The networks are currently as follows:

192.168.0.0/24
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24

I would install 5 network adapter in a PC, one for each network and one as a WAN port. Is this a workable solution?
Any other advice would be appreciated.

[HROAdmin26]

Of course. And if you want an ENT-level solution, there are packages like Vyatta.

[bajangerry]

What about if I am using a Layer 2 switch for all network activity in this location, will I be able to configure a single physical network adapter in the linux box to provide routing between the VLANs if I configure the switch port that the network adapter is connected to to have tagged access to each VLAN? I have been reading about configuring VLANs on network adapters under Linux but I am not sure how that will work with tagged network traffic, is my theory accurate?