Hi,
I have a netgear ddg834gt router. My PC uses a USB dongle to connect. I also have a laptop, which works fine.

Problem is, for some reason, after about an hour of inactivity (for example, if I am downloading / uploading and leave the PC alone) the connection drops.

This is becoming frustrating as I am uploading video files to my website (i am in the process of starting up a company). I leave my PC on to do this, only to return and find it not working. I have looked on the netgear website (and thier http site 192....) and the time out settings are set to "0". According to the site it only happens if you do not have XP service pack 2 installed, I do, so in theory there shouldn't be a problem.

Any suggestions?

Try this first;

Click Start.
Right-click My Computer.
Click Properties.
Click the Hardware tab.
Click Device Manager.
Click the plus sign (+) in front of Network Adapters.
Double-click the name of your Ethernet adapter.
Click the Power Management tab.
Remove the check mark in front of the Allow the computer to turn off this device to save power option.
Restart your computer.

There is not a power management tab on my Netgear adapter...

In that case, have a read of this: Windows power management is turned off when you turn off the WakeUp option for an NDIS wireless network adapter in Windows XP