Hi Chris
Wireless can be a security issue, but most of the wireless routers offer security features, in the form of "access codes" where you create a 10 or 26 digit access code (or key phrase, depending on the manufacturer) that you need to put into your computer in order to use the wireless, or by a process called "MAC address filtering". Every network card made has a unique hardware address (in the form of 00-3e-aa-22-a1 or something similar.) you input these addresses for all your computers and restrict access to only those computers for the wireless.
both work well, but to make sure that you are secure, one of those measures has to be implemented. In some cases, you can implement both.
I've got our house setup for wireless using the keycodes, never had a break in.
when looking for a wireless router, stay with brand names, Dlink, Linksys are the best.
Hope that helps