need help networking laptop and desktop using bart-pe

My problem has been one of software and now of networking. My laptop is running winxp-media center, my desktop is booting through bart-pe at this time. When it is working it uses winxp-professsional. I did a defrag about a week ago on the desktop and then started getting error msgs about different exe files being corrupted. When I cut the machine off, it would not come back up. I have used the bart-pe to make a bootable disk. I can get the computer up and I can see the file directory. When I open the network system up, I can see the shared files on my laptop but they will not open. I am getting invalid file name errors or being told that I don't have administrator privileges. I want to get my data files off the desktop before I lose them so that I can reformat the desktop. I can also see the workgroup name of the desktop from the laptop, but get the no administrator privilege msg. I have connected the to computers with a cable but I don't remember what it is called. Please help! Thanks...Diane