Since you have 5 legit IPs, you could connect up to 5 machines to the modem with a switch or hub (either will work), but you'd lose the security that a firewalling/NATting router gives you.
In terms of switch->router->other PCs, yes- there's no problem with doing that.
I'd go with chanto!'s port-forwarding suggestion though, that will keep all of your machines behind the router.
DMR
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I want 3 machines to have different static IPs that are my external IPs so I can run a ftp server, webserver and a game server.
pc 1= xxx.xxx.xxx.xx1
pc 2= xxx.xxx.xxx.xx2
pc 3= xxx.xxx.xxx.xx3
Man- if you're going to do that you'll have three unprotected machines, running three vulnerable services, sitting out there for anyone to have a whack at.
Unless I'm really being a muppet here (which is quite possible) I think I understand what you want, but what's so bad about using the router and just properly configuring its port-forwarding? Sure, you'll only have 1 static IP on the WAN-facing side of the router, but when you hit that IP in a web browser, the http requests will get sent via port 80 to the Web server; when you FTP to that IP, FTP requests will get routed via port 21 to the FTP server, etc.
As far as static vs dynamic IPs, you can still assign the servers static addresses even if they're behind the router.
DMR
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Usually you don't; you assign the machines on the local network IPs from one of the private, non-routeable ranges like 10. or 192.168. and set the router up for NAT (Network Address Translation). The router will "learn" the IPs you assign to the LAN machines, and by setting up port forwarding as in chanto!'s example, will route both outgoing and incoming requests to the proper destination. The manuals that accompany most routers do a good job of describing how to set everything up, but if you have specific questions just tell us the model of router and we can walk you through it.
DMR
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OK, if you want to specifically use the IPs that you've got and access the machines from the Net that way, I'd install a good software firewall on each of them. You might want to take a look at the Zone Alarm firewall packages from Zone Labs.
DMR
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