Someone please help me......

I am running XP and have two routers:

1. Router 1 (R1) is an ADSL modem conected to my PC via an ethernet
port - this is for internet access

2. Router 2 (R2) is a wireless router connected to my PC via wireless.
Plugged into this router via ethernet is a hard disk - I use this for
back up.

And now the problem....

If R1 ONLY is connected, internet access is fine.

If I now enable the wireless and R2 is connected - I loose internet
access. I can of course see the external hard disk I use for backup.

I can see what is happening here - but I don't know how to fix it. When
R1 is only connected, this is used as the default gateway (192.168.1.1)
for the internet connection. As soon as I enable the wireless, this is
used as the default gateway (192.168.0.4) - but there is only a hard
disk connected to this and hence no internet connection....

So - how do I stop XP from changing from one gateway (192.168.1.1) to
another (192.168.0.4) ??

Thanks.