Corrupt downloads on Panther (windows network) Help!

I have my windows machine connected to my cable modem (WinXP Pro, PIII 750, D Link Ethernet card). I purchased a D Link ethernet card to be able to share the internet connection with my Powerbook (Al 15", OSX 10.3.2), but I'm having problems with my downloads.

When I connect directly my Powerbook to the cable modem, there is no problem, but when I connect through the windows machine (as server), Internet works well, but most of my downloads (no matter from where, apple.com, download.com, poisoned) are corrupt. Sometimes I find myself d/l the same thing 3 or 4 times in order to get it right. Last night I tried to connect dierctly the powerbook, and all works out fine. What could be the cause of this behaviour???? the ethernet card? windows settings? panther settings?

I can't keep the powerbook connected directly all the time.

Thanks in advance