Wireless / Lan interaction problem

[platypus]

As shown below (obviously rendered by Rembrandt), I have 2 pc's on a switch (or a crossover), with one pc on the internet via wireless.

Basically the problem is thus: If I have the LAN (switch or crossover) enabled, the wireless connection doesn't work. It looks as if its connected (I can try and get some screenshots tonight when I get home), but the connection is just dead and no data transfer happens on it at all. If I disable the LAN, hey presto, I can browse. Basically, I'm trying to get the 2nd pc onto the internet (no wireless network card), via sharing the wireless connection, but it just won't work when the LAN is enabled. Any ideas, or notions what I'm doing wrong?

TIA

 

[tolien]

Have you got a default gateway set on the (wired) network card?
How have you got it set up? ICS, the wireless and wired interfaces bridged, something else?
With the two enabled, can the two machines ping whatever's on the other side of the wireless adapter?

It sounds vaguely like the machine's expecting an internet connection at the other end of the wired network connection, and ignoring the wireless one altogether.