Ok, I'll start simple, then go into details afterward, in case the setup matters.

I'm running a PC with windows XP SP2, conneted to the internet through a DSL modem via ethernet cable. What I'm trying to do is connect an Xbox 360 to my computer to share media and internet connectivity through a second NIC I just installed. My original NIC is a Linksys NC100, and the NIC I borrowed from a friend is a Dlink DE528.

The problem is, DHCP won't assign a valid IP address to the second NIC. I know there is no problem with the NIC itself, because I've switched things around and connected through the Dlink NIC - disabling the Linksys to do so - and everything worked fine. But if one NIC has a valid IP, the other will not for some reason.

If it matters, I don't have a crossover cable so I'm using a Gigafast EX800-s 8 port switch and an extra ethernet cable to connect the Xbox, but I don't think that's my problem, either, since I also tried connecting my DSL modem through the switch, with both NICs, and it worked fine.

I tried assigning a static IP to the second NIC (one number higher than the other NIC), and it *showed* to be owrking fine in Network Connections, but still there's no connectivity.

So what am I missing?

You can make this whole thing easier on yourself and get a router. Your DSL modem is only going to give ONE IP. You need to create a LAN that will use private IPs Internally. Since the other device is an XBox that has limited programmability you may not be able to have it setup using Internet Connection Sharing.

However, if you get a router, you can connect the PC and the XBox to the router and shouldn't have a problem.

Thanks for the help, but the first problem is that I'm broke. I'm on disability (the 360 was an early christmas gift from family), and on a very limited income, so a router, unless I can find one for five bucks or less, is (currently) out of the question. I'm working on borrowed equipment already.

Secondly, at this point, I don't really even care if the Xbox connects to to internet through my computer so much, (which I know it can do, there's a section on their website that says it can, but it doesn't tell me much about how to do it) since I can just switch over a cable and make that work. What I really need it to do is connect to my PC for media sharing. But if I'm understanding it right, that still won't happen until my machine recognizes the NIC on the "network".

Look around, you may be able to find a wired router for under $10. I've seen stores like Microcenter advertising them. With your current setup it won't recognize the 2nd NIC.