one to one nat router

[H@WK_EYES]

Can anyone recommend me a software one to one nat router/firewall?

basicly i am going to be setting up a colo box with vmware esxi server installed which will be running 5 vm machines and i have 5 public ip addressed for it.

basicly what i want to do is setup a 6th vm machine which will be used as a nat router/firewall for the 5 other vm machines but i am not sure how to do this?

any recomedations would be greatful

 

[m_cozzy]

Why software? Surely a pix or similar would be the preferred option?
Certainly my esxi server on a /29 is behind an cisco asa.