Cannot Ping Router Sometimes (wierd)

This is a tough one. I think I've tried just about everything. I've even had a Microsoft Certified friend of mine come look at the issue. Although he's not a network guy and recently graduated he still couldn't figure it out. So a BIG KUDOS to those who can. Here's the deal:
I have two computers networked sharing a DSL connection. I am using a router to network them. The router is a Airlink 4 port 10/100 router. One of the computers is a Windows 98SE equipped PC and is located downstairs in my house. The other is a Windows XP PC located upstairs. The windows 98 Machine works fine, will surf the net, can ping the router, can get into router configuration, etc. However, the Windows XP machine cannot surf or even get into router setup. When I ping the router from the XP machine the XP machine will return anywhere from 1 to 3 of the pings successfully. But, never all 4 pings to the router are sucessful. The things I have done are:
-Ping the NIC card on the XP machine (came back fine)
-Put the XP machine downstairs and hooked it to the router. No go, XP machine still could not surf
-Hooked up the XP machine DIRECTLY to the DSL modem,not using the router at all. surfed like a charm, no problems at all.
-Tried changing the ports on the router for the XP machine, still no go. However, the Win98 Machine will work on any port.
-Tried the Windows 98 Machine upstairs, ran just fine through the router.
-Tried disconnecting the Windows 98 Machine and Just had the XP machine hooked to the router, still no go.
-The XP machine (when hooked to the router) can release the IP but cannot renew it. When it goes to renew the IP there is a very long pause then it returns with "unable to contact DHCP server" or something like that.
-Uninstalled the NIC then reinstalled.


There are some setups on the router I did not complete. The reason for this is because it said I should get these numbers from my DSL provider. I called Verizon and they were unable to help/didn't know what I was talking about. The numbers were DNS address, IP address, and Gateway. I tried using the computers IP for the iP address and used the router as the gateway but then the windows 98 machine wouldn't work at all and there was no change in the windows XP machines ability to connect. Here is the info on my connection:

Coppell, Texas Verizon DSL
Always connected
IP: 4.63.71.239

I don't normally give out my IP, but hey if anyone wants to hack into my computer and fix it feel free :) hehe.