One is the file-sharing problem, and that's possibly being caused by the fact that you may not have run the networking wizard on both computers.
Think of the networking aspect as being entirely separate from the wireless internet connection sharing - you must set the network up before your computers can share files. Run the wizard, and make sure that you use the same workgroup name on both machines; by default you'll be offered MSHOME, but you can choose a name of your own if you like. Then ensure that both computers have different individual names "main" and "laptop" for instance. Next, you must enable sharing on any folders or files which you want the other machine to access. You must do this on both computers. For security reasons it's not a good idea to share the root of a drive - don't share the whole of your 'C' drive.
That should get the networking under way, although you may find that if you have a firewall running on either or both of the computers you have to turn it off whilst all this is going on.
As part of the network setup you'll be prompted to say how each machine accesses the internet. Tick the appropriate options and let the wizard complete - at the end of it you should find that you can use the connection on both machines.