I have to be honest, I have never heard of Hardware attacting spam, but nowadays I would rule nothing out,
It never does much harm to update the firmware as it is usually very thoroughly tested before release
As it is a wireless router, I would be tempted to believe that there may well be another wireless network not to far away that may be away that may well be interfering.
Interference can be caused two ways. First, other sources of radio waves such as other 802.11b devices operating on the same channel, microwave ovens (they operate on the same frequency at much higher levels), 2.4 gigahertz cordless phones, and other errant radio transmissions. You can reduce this interference by eliminating the use of these devices or by turning them off.
The second source of interference is "multipathing". When the signal is blocked or hindered between your computer's adapter and the routers' antenna the signal will suffer from multipathing. This causes the signal to deteriorate due to the fact that all signals are not communicating clearly and arriving at different times. Unfortunately, there is not much you can do about this type of interference other than adding better antennas.
You can check your signal strength and also any other wireless networks in the vicinity by downloading
Netstumbler (1.26Mb freeware)
If one of the pcs is running XP,
Select
Start | Run then type
services.msc into the box and hit
OKScroll down the list until you come to
Wireless Zero ConfigurationRight hand click on it and select
Stop, then shut the window
You could try changing channels, so for instance if you are on channel 11, change it to channel 1
One final thing to check is that you have WEP enabled