Loosing connection between server and clients

I am running server 2003 and XP Pro clients and we are loosing packets
terribly. I ran a ping from client to servr and had9% loss overnight.
>From server to client ping I had an 18% loss overnight. We have many
multiuser file shares and they are being kicked off sometimes every
minute.

I installed SP1 a week ago and my problems began. I removed SP1 and
found my ethernet card had changed protocol. I switched over to another
card and reduced packet loss to the above mentioned after all repairs.

Shoul I reinstall the SP1 and then fix the protocol issue or is there
another fix.

Thanks