Slow network speed

I am using a router to share a cable modem connection. On my win98se machine when i check the status on the “internet gateway” icon in the taskbar it says the connection speed is 10Mbps, but it should be 100Mbps like my XP machine. The ethernet connection on the win98 machine is an onboard realtek on a gigabyte GA-7ax board. How do i fix this to get the full 100Mbps connection i should be getting. One last question, is it ok to go ahead and get rid of the firewall software on both machines now that the router is in place? Thanks.