You can manually fill them in just fine; I've done it and it works well. What values you need are dependent on your network and what you are connecting to, so I can't just tell you what to use.

I would suggest doing a DHCP boot and then checking what these values are; from there you could bypass dhcp and set them manually (be careful, of course, that you use a valid IP address and not one that dhcp might give out to another system, DHCP will give out addresses from it's pool and could give out the addres you select if you don't take care to select one not in the pool). Perhaps if you posted what you were using someone could point out what you were doing wrong. Some settings, like a bad mask, would be easy to spot, but others (like a bad DNS value) would not. Also, it would be helpful to know your local network configuration and what you are connecting to,