LAN going slooooooow!

I’ve had this problem with my 2-pc LAN for quite a while. My setup is as follows:
P4 2.8 - WinXP Pro SP1
P3 800 - Win2K Pro SP4
Billion 4-port ADSL router

The lights on my router are green for both PCs, indicating a 100mb/s connection, but the maximum speed I get is about 5mb/s (600kB/s)!!!
Transferring files takes forever!!

I’ve Googled this problem to death, but found no solution :frowning:
Is there some patch or registry setting or something? I have no idea.
Oh, im also using Sygate Personal Firewall, if that makes any difference.

Thanks in advance :disco: