Performance problems with connection sharing

hi.. after many attemps i've finally connected my cable to linux and
made it a route... i can get ping replies from my windows client but
when i try to actually view a page it's very slow....

so i made the following attempt:

in the windows machine i tried dialing pptp directly to cable and
download the following file:
http://www.tucows.co.il/files3/FLStudio501_Install.exe

i got around 180kbps speed

when i tried downloading the same file from the same machine only via
linux router i got 266 bytes!!

when i did desg i saw many messages about:

eth1: setting 100mbps full-duplex based on auto-negotiaited partner
ability 45e1
NETDEV WATCHDOG: eth1: trasmit timed out

my eth1 is edimax realtek 8139 could this be a problem do i need to
change to antoher PCMCIA card?