strange network failure

I have an interesting problem...

Recently I have been having trouble with one of my computers. As a result I have now re-installed windows XP 3 or 4 times since the beginning of the year, with the majority of those times being the last 2 months or so.

Internet connectivity stops working. I get a message that a network cable is disconnected. I cannot use the internet.
Strange because it is a dual booting system and my Linux partition has NO TROUBLE connecting.

After I re-install Windows XP everything works fine. Internet works, I can download, surf, email... I then go through the very lengthy time consuming process of re-installing software and registering licenses so the software can work (some packages make it impossible to just use a key phrase).

Sooner or later the internet stops working in XP. This happened again recently, when I boot to linux it works so I know it is not the hardware.
I tried changing the speed and duplex setting from auto to 10 or 100 mb full or half. No change, no internet connection.
I have tried removing and re-installing the driver for the network adapter.
Even going back to a previous restore point, when the network WAS working does not fix it!

I removed my hard drive and I re-installed XP to a smaller hard drive and, yes, I can connect again.

I do NOT want to go through the process of re-installing software or license rights again. Besides, it may only fail again in a few days/weeks.
I would like to be able to fix this on my XP installation.

How do I ...

1. Find out what is broken and fix it?

2. Stop it from breaking again.? (This will no doubt depend on answer to 1).

One thing that comes to mind... I do not register XP after I install, I just activate it over the net. This option to register it... is it manditory? Could this be the cause?

the system in question...
Cable connection to internet (NOT wireless).
Asus A7V8x, Asus tek/Broadcom 4401 integrated controller (on motherboard) .
XP home. XP service pack 3, I allow all updates to take place as I am notified (except I do not allow iIE 8 to be installed), normally I use firefox.


Thanks