let's simplify this:
First, set up a network where you can get internet on both computers. Do a google search for this, or configure (the wizard doesn't do this) your router to allow WiFi access and choose the channel and WEP (or other) key (so no one else gets in to you network) and get your other computer on the same channel and WEP key. That's half of it!
Now, once your network is up, choose the folders you want to share (right click>Sharing>Choose options)
Now you need to get the IP addresses of the two computers.
(1.)Open a DOS command prompt (ask if you need help with this)
(2.)Type ipconfig and press Enter
(3.)Find the label for your connection or adapter (the IP should be something like xxx.xxx.x.x
After you've done that, go to Start>Run>Type \\IP_of_comp_you_want_to_access>press Enter
Now, the shared files and folders will show up in the window that is opened.
A suggestion: (sp?)
If you are worried about computer space, you can connect a Network Storage Device (that is, if you have about $150) and I think Western Digital makes some. These are hard drives that you can to your router or wireless network that you can simply put things on.