That depends on what you mean by access the file system. If you want to log
on to the linux box, you can use a telnet application. The one I use is
called putty, and you can download it from:
http://www.chiark.greenend.org.uk/~sgtatham/putty
If you meant that you want to access the linux file system from your
window's network neighbourhood, then you need to set up samba on your linux
machine. This comes with your linux distribution, and is free. The windows
machine will then just see it as if it was a share on another windows
machine on the network.
Hope this helps,
Dan.