What would be the main reasons for two NIC's or (eithernet ports) on a server? I bought some serves for small projects and they have two 10/100 ports. Whats the main purposes? ~Thanks

There could be several reasons. I suspect the biggest is, in case you need to have the server connected to multiple subnets. I know we have many servers at work with 4 or more network interfaces in them (usually with the addition of a 4 interface card) because they connect to multiple subnets. If your server is only going to be connected to one network then you'd have a spare in case the first one fried. At least, you could switch over to it faster than if you had to down the server, open it, add another NIC, then close, rack and then fire it up again.

Ohh. I thought Maybe one for internet the other to connect to users that get internet through the server. Never thought about LAN redundancy though.

You can also consider adapter teaming which combines the nics into one virtual pipe doubling the bandwidth to and from the server.

Can I conect two 10/100 NICs into a GIGa net? or is it only guna be 20/200?

The managed switch you connect to has to support one of the teaming protocols. This is not something you can do with an unmanaged switch. Now if your gig switch is managed and supports 10/100/1000 your combined bandwidth would be 40/400 mbps 10mbps full duplex is 20mbps so you double that with two full duplex nics for example.

Ohh. I thought Maybe one for internet the other to connect to users that get internet through the server. Actually, that is another option. In that case you'd have the internet plugged into one NIC and then the other would be plugged into the switch with all the other LAN clients. But, when you consider you can buy a SOHO router for around $40.00 (USD) it doesn't make sense to burden your server with having to do the NAT when you're $40.00 device will.