I'm trying to set up a home network with a new wireless router (LG-ERICSSON WBR-3020). I am using WPA2-PSK encryption with AES. When I enter the passphrase on my macbook air (OSX 10.7.2) it connects flawlessly when given the passphrase, and similarly with an iPad, and iPod touch. On my Windows Vista laptop, when I give the correct passphrase it has "limited or no connectivity." This computer uses an Atheros AR5007EG Wireless Network Adaptor. In the wireless connection properties, all the boxes are checked, including IPv4, IPv6, and Client for Microsoft Networks. (Unchecking IPv6 as some people have suggested does not help). IPv4 is set to obtain an IP address and DNS server automatically.
When I've had trouble like this it normally means the wireless network driver does not support that particular form of network encryption.
You can test this by setting your security to WPA(1) and seeing if the Windows computer connects OK to that.
Also, I'd try disabling any special utilities managing your network, none of them do any more than Windows does, and none of them does it as easily either.
Can you ping computers on your network? If you can't, or the adapter shows 0 packets sent, try downloading the latest drivers for your wireless adapter. After Windows XP, Windows got proficient at connecting to wireless networks out of the box, but in rare cases some adapters aren't fully supported by Windows.
Edit: If that doesn't work, @music2myear is probably right: your adapter doesn't support WPA2 encryption.
I have a wireless router, and I want a difficult password that is still, in a way, easy to remember.
I came up with this idea to take the MD5, SHA-1, SHA-256, or whatever hash of a common English word, such as "superuser" and use the hash as the WPA2 key.
For example, let's say that "superuser" was my word of choice. If I chose SHA-1 has my hash, I would then set up my WPA2 key to be8e67bb26b358e2ed20fe552ed6fb832f397a507d.
Is this a secure practice? Common English words are being used--in a way--in the key, but the key itself is actually a long, complex hexadecimal string.
Unless you reveal the method of how you generated you "long WPA2" key (which you just did), it is just a random string of text which would normally be pretty secure. On the other hand, if someone knew that you were using "a common English word" and used a hash of that word as the key, anyone could quickly generate a sequence of hashes from a dictionary and break your password pretty quickly.
If you are looking for a "difficult password that is still easy to remember" why don't you come up with a longer pass phrase that means something to you but not easily guessed by anybody else. Start with a phrase (i.e. sequence of words, sentence, etc), mix in a sequence of digits that mean something to you (apart from birthdays, phone numbers, etc), and generate a long key that is "easy to remember" that way.
It is as secure as any other key as long as you do not tell anyone.
At the end of the day, your key will be using 0-9, a-f... which is actually only gives 16 possible characters instead of just a-z which would give 26. Therefore, if you think you are being smart and tell someone "I am using SHA-1", you are actually cutting down their brute force combinations by quite a few.
Personally, I think you would be a lot better off just having a normal long word/s with a mix of case, then throw in some random numbers and symbols.
It is safe as long as nobody can possibly figure out the method. This of course includes bragging about it in the office, but also traces of any kind you may leave behind. As an example, if you are to connect a random user to your network, you'll probably use some kind of client-side application to generate the hash. If the random user then notices that there's an echo "superuser" | sha1sum in the log it's not too hard to add the two together.
echo "superuser" | sha1sum
Seeing as you'd have to generate the hash externally, much of the convenience disappears. Generally I'd say that hashing a common word might be an acceptable way to quickly generate a semi-random key, but the key must still be copied or remembered when entering to not pose a weakness.
The only other gain I can think of is that the key/phrase/password can be easily reproduced if lost. If above security-measures are taken I see no reason not to use hashed words as keys.