Win2k server - which firewall is best?

[MnM]

I have Win2k server running on a machine that connects to the internet.
Now I am after a softare firewall. It doesnt matter from the LAN to WAN side (so users can do pretty much anything). What I want is to block people from getting in (WAN to LAN).
Which product do you recommend?

Thanks.

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-== MnM ==-