Is the "LAN connector that came on the motherboard" an actual NIC that is on the motherboard? Or are you talking about an onboard LAN connector? If it's onboard, then you will have to find the driver. Normally the mobo will come with a CD that will have various drivers on it, you will just have to put it in the drive, and click on it, and it should work fine.
If you don't have the CD that the motherboard came with, you should be able to find it on the vendor's site. Go to the website of the company that made the motherboard, and see if you can find the drivers for it. If they're not on the website, then you can always try google to find them.