Hi to all experts !
Well I come to you very humbly after having spent hours and hours of unsuccessful nightly work.
The problem is the following : how to access the internet from a station (PC1) wifi linked to a linux station (PC2) itself Ethernet linked (cable) to a hub connected to a modem router ???

PC 1 ---- wifi ---- PC 2 ---- Hub ---- PC x
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''''''''''''''''''''''''''''''''''''''''''''''''''''''''Modem-router
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''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''Internet

The IP configuration of the whole stuff is the following :

PC 1
running Win XP (OK, OK, please...)
Wifi PCIcard : DLink 520+
IP adress 192.168.0.4, netmask 255.255.255.0

PC 2
running Linux Mandrake 9.2
First interface : wlan0
= Wifi PCIcard : DLink 520+ (works perfectly under Mandrake 9.2 after module compilation !)
IP adress 192.168.0.2 netmask 255.255.255.0

Second interface : eth0
= Ethernet card (SIS chip on Motherboard)
IP adress 192.168.1.3 netmask 255.255.255.0
Gateway 192.168.1.1

Modem Router
Bewan ADSL Cx Ethernet modem router
IP adress 192.168.1.1 (THE gateway)

I can ping 192.168.0.2 (wlan0 of PC2) from 192.168.0.4 (PC1)
I can ping 192.168.1.1 (router) from 192.168.1.3 (eth0 of PC2)
I can't ping 192.168.1.3 (PC2) from 192.168.0.4 (PC1)
and of course
I can't ping 192.168.1.1 (router) from 192.168.0.4 (PC1) and of course access the internet, this is the main problem!

The only thing that worked was a successfull ping on 192.168.1.3 (Ethernet on PC2) from 192.168.0.4 (PC1) after having launched a ARP Proxy on eth0 and wlan0. But 192.168.1.1 (router) remained invisible for PC1 even with the ARP proxy running.

I've tried many combinations in the routing table of PC2 using "route add..." but obviously not the good one* ! I feel it is a routing problem but... Would a bridge between the subnets be usefull ? Heeeeeeeelp !
* the default route is defined as using the gateway 192.168.1.1

The first relevant reply wins my eternal gratitude !

N.B : of course I could add a second ethernet card on PC2 and use it as a residential gateway but it would mean full time power for PC2. Moreover, now I've launched out a challenge to myself I must find a way to succeed... and find peacefull nights !

Thanks to everybody

Hum ... the scheme does not appear as I drew it...
The link to the modem router and internet starts from Hub and not PC1 !

Anybody interested in this issue ?

you do know you're asking PC2 to act as a wireless access point/router, don't you? Do you have it configured to do that?

i have a home network set up with a wireless access point (AP) plugged into a router. All the wireless PCs connect to the router thru the AP; the rest of the PCs are ethernet cable to the router. The router handles all the routing/dhcp stuff as well as acting as a NAT firewall.