via a wireless router doesn't mean you can share files between the two machines. You'll need to run the Networking wizard on both computers in order to do that.
The wizard will step you through the process, and all you need to remember is that both computers must belong to the same workgroup - by default you'll be offered MSHOME, and unless you particularly want to use another name you may as well accept that. You can give each computer its own name on the network, 'Main' and 'Laptop' for instance, and you must enable sharing on the files and/or folders which you want each machine to show to the other. In networking practice it isn't a good idea to share the root of a drive from the security point of view, so don't share the whole of your C drive - just the folders that you'll be using.
You enable sharing by right-clicking on the file or folder and selecting 'sharing and security'. This will open a dialogue box in which you can select sharing options.