networking question/help

I have a network at home, 3 computers and a laptop- there are times
when the laptop with a wireless card can see and trade files with the
other computers but not surf the net. I fixed it but I'd like to know
what causes that as I'm not quite sure what I did to fix it. All the
desktops run windows XP and the laptop has windows xp pro.
second question:

I have a thinkpad with a 3com 11mb card. I just got a Proxim 11a/b/g
ComboCard Gold card so I could connect to faster networks. The signal
on this card around my house is about half what the 3com card is. Why
is that? Is it possible the card doesn't like my access point (a
buffalo air station that is a few years old.

Any ideas? I'm certainly not going to get a new access point for this
card if the card itself has such a poor signal. Does the access point
and the card combo make a difference?

thanks

Nancy-
p.s to email take out the nospam in the address above