You'll have to access the Vaio's web menu using Internet Explorer (Try inputing this into the Address toolbar of IE-- 10.0.1.1 without the www) from your computer and somewhere on there should be a security menu where you can input all this. You can assign passwords, set encryption or a set amount of IP addresses so if you know you only have two PCs, you can set it to just that to prevent someone from getting on.
If that doesn't work, the settings can be done over the CD setup wizard that came with the Sony VAIO LAN access point. It must be accessed using one of these two ways.
Does your VAIO look like this?