If you can attach to another site's wireless -- like your own -- then the unit is probably working properly.

It's probably some form of security. There's lots of reasons APs don't complete a connection to a wireless computer:

1. There's an encryption system in use you can't get into.
2. The access point only communicates with a certain set of MAC addresses and your unit does not have one of them.
3. There is no DHCP in use; all units are assued to statically assign an IP address.
4. The signal is weak and cutting in and out too much to sustain a good connection.

You said you can get a good signal and that it's not encrypted. So my guess is that #2 above is in place: your unit does not have one of the approved MAC addresses. If that's true, then you are SOL.

If it's #3 above, you could try manually assigning an IP address in a standard range, say 192.168.1.x. That's a needle in the haystack proposition, however. You are probably SOL there too.