LAN ping issues

Internal LAN ping issues. Home network layout.

router:
Linksys WRK54G
Gateway/switch
Broadcasting SSID
Channel 3
WPA/TKIP encryption
Enabled MAC filering
Shared Key mode
Disabled DHCP
192.168.0.1

comp1: laptop
Onboard DELL 1350 WLAN MiniPCI card
WinXP Home SP1
192.168.0.5

comp2: laptop
NetGear WG511v1 PCMCIA card
WinXP Home SP2
Disable WinXP firewall
Disabled WinXP WZC service
Using NetGear connection utility
192.168.0.3

comp3: desktop
Onboard network adaptor
WinXP Home SP2
192.168.0.6

comp4: desktop
Onboard network adaptor
WinXP Home SP1
192.168.0.4

Problem:

comp1 can ping comp3, comp4, router
comp1 receives Request time out from comp2
comp1 can ping public IPs

comp2 receives Request time out from comp1/3/4
comp2 can ping router
comp2 can ping public IPs

comp3/4 are the same as comp1

Only when I ping from comp2 to the others at the same time
I'm executing the ping from the others to comp2 will the
machines respond to eachother. The router always responds.
The time outs aren't consistent. It can happen after 5 minutes
or after 30 minutes. I can never tell when comp1 will apparently
looks as if it dropped off the LAN. It takes the double ping
to revive the LAN connection even though I can ping public IPs.

Attempted solutions with no success.
Downloaded and installed latest drivers and patches for everything.
Reflashed the router's firmware a few times.
Uninstall NetGear utility and use WZC service on comp2.
Different channels.
Moved router location.
Turned off encryption (but I want to use it).

Reasons?
router problem?
PCMCIA card bus problem?
PCMCIA card problem?
PCMCIA card drivers and utility software?
WinXP?


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