Question : Download causes connection speed to drop

I'm sorry for asking what is likely to be a common question, but I can't find the right answer anywhere.

I'm on a cable broadband connection. The results of www.speedtest.net are as follows:

Ping: 21ms
Download speed: 2.43Mb/s
Upload speed: 0.45Mb/s

Now, if I try to download anything at all, the download speed drops significantly. The speed never seems to go above 250-280kb/s for the file itself that is being downloaded, and if I attempt to run the test at www.speedtest.net while I am downloading, it suddenly produces far worse results, eg:

Ping: 212ms
Download speed: 0.38Mb/s
Upload speed: 0.35Mb/s

Is that normal? I can on occasion, when I first start downloading a file, get speeds of just above 1Mb/s, but that rarely lasts more than a few minutes before it drops back to the 280kb/s mark.

The setup is that the cable modem connects to a D-Link router (DIR-615), there is a wireless connection available from that, but the desktop PC on which I attempt to download files and which is relevant to this question is connected to the router via a cable.

I'm not sure what further info I need to put in here but if anyone can start off helping me out that would be great. The ISP, incidentally, report no problem on the line or anything like that.

Thanks.

Answer : Download causes connection speed to drop

Install the AD by running dcpromo on the new hardware.
Install DNS. If the existing DNS is AD intergrated then the new DNS will pick up all the entries from AD.
Check replicatin is happening between both the DC's.
Transfer FSMO to new server.
Ponit the exchange to new server in NIC.