Vista - Only local connection

I have a Dell Inspiron 1720 with Windows Vista
I'm trying to connect to some unsecure wireless networks at a friend's house for the first time and am only able to connect with local access.
I try diagnose and repair and it says that there are no issues. Three other computers are connecting to the internet just fine.
They signal is good, and there is supposedly data being sent and received but no programs will connect to the internet.
This issue has never happened before. I regularly run a registry cleaner and tried restoring to a backup from a couple days ago and that didn't help.

also,
i was unable to ping a website
i disabled windows firewall and exited my antivirus (avg)
i haven't installed anything new since the last time i connected to an unsecure network

Here are the other things I've tried:
-disabling the IP helper service
-disabling IPv6 (the mac i'm using at the moment is connecting fine using ipv6)
-disabling the dhcp broadcast flag
-reinstalling the drivers
-using a usb wifi card
-manually setting the ipv4 dns servers

none of this has worked.

i went to an internet cafe and was able to connect there, but still can't connect at my friend's house, where three other computers are working just fine

please help!

You haven't bothered filling out your system specs so we haven't a clue what type of machine you have or what version of Vista you use.
It's also possible that your friend is only allowed so many connections on his line so your's is being denied.
Those are my thoughts on your problem maybe someone else will have a better idea and be able to help, you could help them by filling in your specs so they know what they are dealing with.

As I said in the first post, I have a Dell Inspiron 1720.

I have Vista Home with SP2.

What other specs do you want?
Even if the other computers are off mine still doesn't connect

Here is the result of ipconfig

Microsoft Windows [Version 6.0.6002]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.

C:\Users\Alix>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : Alix-Laptop
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No

Wireless LAN adapter Wireless Network Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Dell Wireless 1395 WLAN Mini-Card
Physical Address. . . . . . . . . : 00-1F-E1-9A-AE-59
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Autoconfiguration IPv4 Address. . : 169.254.20.5(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . :
NetBIOS over Tcpip. . . . . . . . : Enabled

Tunnel adapter Local Area Connection* 6:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : isatap.{AB877721-6EBE-4F36-A9ED-39778B04D
68E}
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter Local Area Connection* 7:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : 02-00-54-55-4E-01
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Looks like you're not getting a DHCP address from your friends router.

Can you confirm DHCP is indeed enabled?
Can you find out what the subnet of the Wireless LAN is? If so can you manually set an IP address (ensuring no IP's conflict with currently connected devices)
Could it be possible that although the wireless is unsecure from an encryption perspective that something like MAC address filtering isn't enabled thus restricting access only to authorised machines.

This was actually at the public library, where it also doesn't work.

How do I confirm that DHCP is enabled? I disabled the DHCP broadcast in the registry, and enabled the broadcast toggle.

I tried manually setting an ip address using the info from my friend's mac and that didn't work either.

DHCP is enabled on your laptop as per your IP Config, but would be worth a double check that DHCP is running from the router/access point, in the case of the library this indeed would be enabled.

Check in Services that DHCP Client is enabled and started (Start > Run > services.msc or right click computer > manage > services)

I assume you tried ipconfig /release and then ipconfig /renew since you already seem familiar with ipconfig

It is enabled for automatic and started
I actually hadn't tried release and renew
I'm not on that connection now so I can't try it but will later