laptops disconnect each other

before we started experiencing this problem, my sister had an ibm laptop
with a pcmia wireless card and I had an acer with a built in wlan. Wireless
worked ok no issues at all. Occasionally, when the wireless router was
offline I would see her laptop broadcasting and even establishing a peer
connection.

That was until she went and got another brand of acer laptop. Both laptops
would be online, working then suddenly they would both lose internet
connectivity. I can ping other wired computers in my lan, I can ping the net
from my other wired computers but the laptop just won't ping outside the
lan. It stays this way for a while then it starts working again, after about
15mins it loses outside connectivity again. I turned my wireless adapter off
and the problem went away on the other laptop.

I'm baffled about why this is happening. Is it because the laptops are
interfering with each other? or the wireless router is getting confused?
It's a dlink 524




Suburban