Are both connected to DG834 wirelessly?
do you have access control switched on?
If the laptop is listed in access control & access control is on it
will connect,
If laptop is not listed in access control but access control is not
switched on then laptop will conect.
Open settings on the DG834 through Internet Explorer, address should
be
http://192.168.0.1/start.htm,
got to LAN IP setup add your main pc as 192.168.0.2, name & enter macc
code,
enter second pc as 192.168.0.3, name & enter macc code
Go to wireless settings and click setup access list
add new staion manually, use names & macc codes of the 2 pc's
turn access control on
In control panel on you xp pc go to network connections & sellect your
connection,
click properties & highlight internet properties then click properties
button
Select radio button "use following IP address" and enter 192:168:0:2
or 3 which ever way you numbered them (xp or vist)
for subnet enter 255:255:255:0
Default gateway 192:168:0:1
Prefered DNS 192:168:0:1
then OK all and maybe restart.
For the vista pc I have no idea of settings on the pc I don't have it.
If you haven't already been here
http://kbserver.netgear.com/kb_web_files/n101649.asp
it may be useful, your router is listed.
all above IP addresses are asuming your on SKY broadband, you never
said.
Good luck