Poor upload performance on LAN to Windows 2003 Server

Does anyone know why copying to (uploading) to a Windows 2003 Server is much
slower than copying from (downloading)?

For example, I have a 100MB file which when copied TO the server takes
around 45 seconds. If I copy the same file from the server (download) it
takes around 10 seconds.

I use Teracopy to copy files and this reports an upload speed of 1.6MB/s
while the download speed is 8.6MB/s.

The server is on the same 100Mb LAN segment as my laptop.

Can anyone enlighten me on this?

Thanks,