Internet Problems w/ XP and LAN's

I have a small LAN using a Linksys router with a DSL WAN
plugged into it. I have 2 Win98 computers always running
and they work flawlessly. I plug my laptop into the LAN
about once a week to keep up with Windows Updates and
Nortons virus definitions. About May 4 or so about the
time the Sasser scare came about I hooked the Laptop
w/WinXP up to LAN and did the updates and NAV definitions.
The next day I tryed to get on the internet with the
Laptop and I couldn't get on with the LAN. I could connect
with the modem but who needs 56k. I tried everything,
checked for virus ran SpyBot and Adaware but I can't get
on the internet. The LAN is there and I can see my IP
address of the Linksys router and I can ping my router and
when I tried to ping Yahoo or Google it sometimes go thru
at 100% and sometimes 50%. Since this started I have tried
to put 2 other XP computers on the LAN and they do the
same thing. I'm not sure if this has anything to do with
the Sasser bug but it did start about the same time. The
first time it happened on the Laptop I used System Restore
and put it back to the day before and everything worked
but whatever it had it got it back and I still don't have
internet on my Laptop. If I've seem 3 XP machines that
this has effected how many more are there out there?