Vista - Can't share internet connection (Vista-XP)

This is puzzling:
I have a Vista PC with a DSL connexion and an XP notebook PC connected
through Ethernet. While both PCs see each other, manage to share files
etc... there's no way to access the Internet on the notebook. What is
strange is that if you don't assign an IP address (leaving it dynamic) to
either network cards, the XP notebook signals a limited or inexistant
connectivity (while you can see and share files both ways all along, ping,
....), that until you do assign an IP adress to both network cards and a
gateway on the notebook, then it all looks connected and fine, but either
way there's no internet connexion on the XP PC. I've followed carefully the
instructions to share an internet connexion as explained in Vista's help,
checking the box (roughly translated from French) "allow other computers to
access this PC through the Internet" (which does seem a bit inapropriate, as
if other PCs on the internet could access my PC?), so is there any
explanation for this problem?

My mistake: understand the checkbox as saying "Let other users of the
network access the internet through this connection".

"Sergio Millich" <millichs@iprolink.ch> a écrit dans le message de
news:AE2A74EF-643D-45EA-95AC-A280809F48D5@microsoft.com...
> This is puzzling:
> I have a Vista PC with a DSL connexion and an XP notebook PC connected
> through Ethernet. While both PCs see each other, manage to share files
> etc... there's no way to access the Internet on the notebook. What is
> strange is that if you don't assign an IP address (leaving it dynamic) to
> either network cards, the XP notebook signals a limited or inexistant
> connectivity (while you can see and share files both ways all along, ping,
> ...), that until you do assign an IP adress to both network cards and a
> gateway on the notebook, then it all looks connected and fine, but either
> way there's no internet connexion on the XP PC. I've followed carefully
> the instructions to share an internet connexion as explained in Vista's
> help, checking the box (roughly translated from French) "allow other
> computers to access this PC through the Internet" (which does seem a bit
> inapropriate, as if other PCs on the internet could access my PC?), so is
> there any explanation for this problem?