I've got a Linux machine set up as a server on the network, with the Windows desktop and the laptop all sharing files, folders, printers, etc with it and each other.
As bnt says, you need to set up Samba. There are some useful sites around that explain how - Google is your friend.
I gave up on Ubuntu, though. It didn't suit my temper or temperament. I use Fedora, which "just works". The Linux box also has Mandriva, Debian, Mepis, Kubuntu, SuSe and Knoppix on it - but all of those stopped working when the video card popped its clogs and I replaced it with a different brand and model. I have to remove the drivers for the old card and insert the drivers for the new one before the GUI display will work, and that's a right faff. Fedora worked it out for itself, and did it for me.
The Linux GRUB bootloader will start any number of different Linux and/or Windows distributions. It's also easy to edit, and you can make whichever operating system you like the "default" that it will start after a suitable pause.
There is another Linux bootloader (I forget the name - Lilo or some such, I think). I tried it a while ago and couldn't get it to work so I went back to GRUB.