Network and printer issues (two seperate problems)

Ok im stuck and unless im doing something realy stupid i dont see what ive done wrong / why its not working.
setting up broadband / connection sharing for my neighbors easy enougth ADSL modem / router (with usb for one computer), so the main PC is connected find via the router now rather than the BT adsl modem it used to use. = win
but (there always is)
The second computer (being connected via eithernet) wont connect.. at all .. the router doesnt even seem to pick it up.
*cry*

Specs
this is all approx because i looked at its insides but forgot to check in windows
OS: Windows XP SP2
Processor: 1GHZ min (its a pretty sexy mother board so going by the size of the heat sink and general coolness of the board)
RAM: 256mb-512mb (couldnt see the side of the ram for a sticker)
Attempts Made
#1
Upstairs Computer: ON
Upstairs Connection: Working fine, google, live journal, msn, kazaa (dont ask) are all fine
Downstairs: on board eithernet, cable running from there to router, congifured to auto detect proxy settings.
Downstairs connection: not working T_T
#2
Upstairs Computer: ON
Upstairs Connection: Working fine, google, live journal, msn, kazaa (dont ask) are all fine
Downstairs: on board eithernet, cable running from there to router, used windows networking wizard thing, in whatever the first option is (connects directly to the internet)
Downstairs connection: no luck
#2
Upstairs Computer: ON
Upstairs Connection: Working fine, google, live journal, msn, kazaa (dont ask) are all fine
Downstairs: on board eithernet, cable running from there to router, used windows networking wizard thing, second option this time (connects via a gateway)
Downstairs connection: again not working
#4
Upstairs Computer: OFF
Downstairs: on board eithernet again.
Downstairs connection: still not working
repeat all this for the network card i added in (which i know works)

SO...
This leave me with
+ one working computer
+ being paid for something that isnt done properly yet (feel bad ><)

- possibility that the 15m cable i have is broke
- that ive done something stupid to make it not work.

Also
Anyone have an Epson printer cant tell you the model exactly, its an ink jet (photo) model of some kind, that has basicly decided not to print in colour anymore.. even when they put in a new cartridge .... any ideas cause im ment to try and help with that as well.

hm, maybe i misunderstood, so please explain:
the PC upstairs is hooked to a ethernetrouter or some USBdevice?
is the PC downstairs set up for DHCP ?
is your network working at all? (see the shares or ping the other PC)

here's what i would do:

#1 open a dosbox on both PCs, enter ipconfig /all to find the IPadresses of both ethernet adapters. same network?

#2 if the upstairs PC says something like PPP-interface then the USBdevice is not routing and you need to set up connection sharing (hm, you said you did...)

#3 try not to ping but to tracert the other PC, pings are often blocked by firewalls. hook them up to the same workgroup, share a directory on each chekc wether they can see each other

#4 ping (or tracert your router (most likely 192.168.0.1))

#5 disable your firewalls make your you physicaly cut the connection to the internet before you do repeat #3

#6 post results here, or drop me a note on icq

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