Having problems with my connection.

As I live in a non cable area, my broadband is through BT line.

I'm with Virgin and I'm using the Netgear DG834G (54) Router.

Now a friend has just wiped my PC and fittted a new bigger Hard Drive. My PC ain't wireless enabled, but have a Netgear 108mps adaptor. Now it's never been a fast connection, but it's doing my head in now. I'm getting a pathetic ONE meg download speed and 0.38 upload! I took my PC downstairs and ran it through the ethernet cable and I got 5/6 Meg! Plugged adaptor back in, back to 1 meg again. Spoke to Virgin and my line is fine and can support upto 16meg apparantly. Tried changing channel etc, no better.....

Anyone know what could be the problem or suggest what I can try? Router? PC? Virgin?