Question : Networking problems windows 7, typing on computer B appears on computer A

New network setup. Cable(cable connect) internet to modem, cable from modem to linksys wrt160N wireless router, cable from router to computer A(dell desktop xps 8100).  Ethernet cable from router to computer B(dell desktop  dimension 8400).  HP laptop connected via wireless connection.
Computer A-windows 7 home
Computer B-windows 7 home
Laptop-windows xp pro
The problem I am having is whenever I type anything on computer B-type in search bar or typing email message, the typing appears in any URL search bar  on computer A.  For example if I have IE or firefox open on computer A, type an email message on computer B, the message shows up in the searchbar on computer A.  If a website is open with any boxes where you type anything, the message appears in it.
Does not happen with laptop.  have contacted linksys 4x, upgraded firmware,rebooted numerous times, still same issues, they have no suggestions.
I turned off file sharing but no effect.
I also have mcaffee internet security, contacted them, they said not issue with their program.

Anyone have any thoughts or heard of this?

Answer : Networking problems windows 7, typing on computer B appears on computer A

this doesn't have anything to do with networking, or antivirus, or windows for that matter.  wireless keyboards operate on a similar frequency to your wireless internet, but they don't relate to each other any more than that.  if you got rid of the wireless networking, your problem will still be there.

a wireless keyboard transmits your keystrokes thru the air, to a receiver that usually gets plugged in by usb.  these combinations of keyboard/receiver can be either "wireless" or "bluetooth".

bluetooth is a little more secure, in that it's hard to get 2 keyboards paired with the same one receiver.  

(below this line, when i say wireless, i am referring to wireless keyboards/mice now and not networking, they are not the same)

wireless is different in that it will accept almost anything on the same frequency.  

so, you must have:
- a wireless receiver plugged into computer-A and computer-B.  
- the keyboard at computer-B is paired with the receiver on computer-B (correctly)
- the keyboard at computer-B is also paired with the receiver on computer-A.  
- the keyboard at computer-A is paired with the receiver at computer-A. (correctly)
- (you might not even have a wireless keyboard at A, but it at least does have a receiver)
- the laptop is unaffected because it's either too far away, or doesn't have a wireless receiver