Awkward WPA2 Issue

Yesterday I was at my brother's, trying to fix a WiFi problem he had for the past six months. The problem existed ever since I set up the wireless network at his house, which probably says something about me :(.

Anyway, the problem is like that: the network works fine with the PC connected to it via cable, and with our Nokia smartphones connected to it via WiFi. Also, a PS3 device is connected wirelessly.
The only device not working properly is a Dell laptop. The laptop was able to connect to the network after a long time, and then only web browsing worked. No instant messenger, no e-mail, no file-sharing. Only the web, and quite slow.

I eliminated the possibility the problem is around open ports and/or port forwarding, after messing with it for about an hour or so. I also noticed some things started working once I disabled the Windows firewall.
Also, everything worked perfectly when the firewall was on, and we used a neighbor's unsecured wireless network.

Then it hit me that the problem might be in the network security. After few minutes I had everything working perfectly: changed the security setting from WPA2 to WPA, and that's it!

I hate to think that some problems are voodoo problems, but this one had all the symptoms. Until today I found out this is a well known issue with Dell laptops. Someone I consider an expert explained:

1. You can try and upgrade the driver. But it doesn't always work.
2. You can reduce security to WPA, but that, as we all know, means the network is hack-able.
3. You can use an external WiFi NIC.

Too bad I didn't know it on the first place. Considering the situation, I'll leave the network with WPA security and hope for the best.