To test the security of your firewall/network such as to verify if you have any common ports which are open to the outside world, file shares that are visible, and so on, check out this site: GRC Shields UP
Just like the site linked to above, GRC also has a page that generates long random passwords that could be used for wireless security: High Security Password Generator
As others pointed out the best defense is to use a layered approach. That includes using a router that has SPI and updated with the latest firmware. For wireless, it should be secured by WPA (minimum, WPA2 with AES preferred) using the long passwords as prescribed above. It also helps to disable SSID wireless broadcast, enable MAC address filtering, disable DHCP, and disable UPnP relying instead on manually forwarded ports that are used by applications that you know you are using.
For the PC/Workstation, it helps to have a combination of software firewall, anti-virus, anti-spyware software running.
On the software side of things, an added layer of defense would be to use Firefox with extensions such as NoScript, Adblock with Filterset.Update, etc. This should block those 3rd party sites that can potentially carry or link to payloads that can install nasties on your computer. Of course the PC OS AND
the software running on it (such as Office, etc.) should be up to date with patches. For example, Microsoft has just released patches for Excel and Outlook (from versions 2000 onwards) last week... You can update your Office by visiting Microsoft's Office Update Site
and selecting the Office Update link (upper right hand corner, 3rd link).
Securing your PC has become almost a full-time job nowadays...