I assume that you are running the 64-bit version of Xubuntu... Check to see if your processor supports VT-x or VT-d,... If so do a couple of things...
(This assumes the specs were for the notebook)
From a terminal;
sudo apt-get install synaptic
(trust me, you'll like synaptic better than the "software center")
Using synaptic,... if your processor supports VT-x or VT-d, install KVM. If not, install VirtualBox by going to the Oracle website for it... downloading it, and installing it with something like;
sudo dpkg -i name-of-the-oracle-virtualbox-package.deb
Set up a virtual machine for your Windows programming exercises (your'll need the Windows install discs)... either KVM or VirtualBox.
For the desktop, install synaptic as above, and from there, install the packages for SAMBA server...
If either of you are running Win7,... be aware that you'll need to make tweaks to your SAMBA server config to get Win7 to cooperate (MS likes to break things).
If the desktop is acting as the server,... use SAMBA to make the files/directories you want be shareable...
SAMBA is going to take some work to understand and set up right, and I might suggest using one of the web-based admin utilities to administer it (however, you might still need to hand-tweak your configs). You can find and install them using synaptic.