We have an existing wired network at our home using a Linksys router. Right
now it connects 2 desktop systems and 1 portable system. We're on Road
Runner cable.

I just got a new portable with built-in wireless capability. We're not
really interested in making all of the computers wireless since they are
desktop systems and stay in the same place. We would like to be able to use
the wireless on the new portable.

Can we "add" a wireless router to the existing wired router that is already
set up? If so, what security issues would we need to be aware of? Would
adding a wireless router disturb the security that already exists for the
other 2 computers?

Any tips or advice is appreciated.