Using 2 modem question??

[tuffpro]

I want to run 2 modems on my home network.
I want one of the modems to work on my desktop only so that it can be used specifically for downloading from a news server at 10 Meg
The other modem is to be used as part of my home network, so that I can access files on my desktop from my laptop & general internet usage for the laptop only.
My problem is that I can’t get the desktop to use the 10meg modem specifically for downloading.
The desktop is connected directly to the 10meg modem via Ethernet or the USB connection. But because I need to access the desktops files via my home network I also have a wireless USB adaptor plugged into the desktop.
So what happens is when I turn on the desktop it always uses the home network modem as the default? So any down loading I start goes through this modem rather than the 10 Meg modem.
I do not want to use the 10 Meg modem for the home network.
Home network modem for legal activities surfing, email, home networking etc (from Laptop Only)
10 Meg for downloading DVDs MP3s, Bit torrent, news server etc (from Desktop Only)
HOW DO I GET THE DESKTOP TO NOT TO USE THE HOME NETWORK MODEM FOR DOWNLOADING?
I know I can sit at the desktop & disable the home network modem or turn it of, and then start my downloading software which will see the 10meg modem (as it’s the only one available).
Whats the way to do this automatically?

Windows XP pro
McAffe security centre
Belkin wireless router
Downloading from Newsbin Pro