bandwidth problems [Linux 2.4.20] [iptables 1.2.7a]

[<root@scheuchenstuel.com>]

Hi!
 
My configuration:
=================

O-------------o    O-----------------------o
|    WinXP    |    |    eth0     |   eth1  |
| 10.10.1.100 |----| 10.10.1.254 | D H C P |----INTERNET
|             |    |             |         |
O-------------o    O-----------------------o
  My Computer           My NAT-Computer

NAT-Computer:
  Linux 2.4.20-4GB
  load average: 0.08, 0.05, 0.06
  iptables v1.2.7a
All the NICs I use are 3com 3C905-TX

When I do some bandwidth tests on the NAT-Computer
(provider's service page) my bandwidth is about 1MBit/second
When I do the same on my computer I only get about 100kbit/second

Now I wonder if there are any problems with my configuration...?
Would be nice if you could help me...

Thanks in advance
Florian St.

Root(AT)scheuchenstuel(DOT)com


My iptables-configuration:
==========================

############################################################################
######

#!/bin/bash
#

modprobe iptable_nat
echo 1 > /proc/sys/net/ipv4/ip_forward

########## CLEARING TABLES
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X

########## SETTING POLICIES
iptables -P INPUT DROP
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP

########## NAT
iptables -A INPUT -i eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

########## LOOPBACK SETTINGS
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -s 127.0.0.1/32 -j ACCEPT

########## EXTERNAL OPEN PORTS
iptables -A INPUT -i eth1 -p tcp --dport 80 -j ACCEPT

########## INTERNAL OPEN PORTS
iptables -A INPUT -s 10.10.1.100/32 -j ACCEPT

######### NAT FORWARDING
iptables -A FORWARD -s 10.10.1.100/32 -j ACCEPT
iptables -A FORWARD -d 10.10.1.100/32 -j ACCEPT

############################################################################
######