Help sharing files over a router

I have an 12gb file on my desktop running windows xp. I desperately need this file on my laptop running windows 7 home 64 bit

I have a router. The setup is as follows:

1) the Ethernet cable from the modem is connected to the internet port in it.
2) The laptop and desktop are connected to the modem via an ethernet cable.

How do i get the 12 gb file from the desktop running windows xp to the laptop running windows 7.

Please can someone help me.

I appreciate all answers.
Thank you
My regards,
Sagooding.