Why of course you can share files.
Here's what you'll need to do:
First off, turn off any software firewalls you may be running. You'll have to configure them later on once you get the network setup.
Next, go to the Control panel and start the Network setup wizard. Follow the OSD. When it asks if you want to turn on the file and printer sharing option, select yes or on (whatever it is, hehe).
You'll need to do this to each computer you want to share files with. You'll also need to make sure that all PC's are on the same workgroup. If they're all WinXP, leave the default of MSHOME.
Then just right click on the folder you want to share and enable sharing or place the files you wish to share in your shared documents folder.