If he wants to synchronise the two PCs, then clever stuff is needed.
If he just wants to be able to copy files from one, using the other, then it's very easy.
I'm sure the link SD gave will do it. Basically,
1. Set the relevant folders as "shared",
2. Run the "Network Setup Wizard" (don't bother with the create a disk bit).
If you want to be imaginative, call the network something other than the MS default suggestion.
3. Use Explorer, "My Network Places", "Entire Network", "Microsoft Windows Network", and then find the network and the other machine(s) .
Takes a few minutes.
You can also connect to Linux machines - and maybe even Macs - like that.