No, that's not the MAC address. When you type in your passkey, it should also generate a number/letter combination. It should look like: 7adwQ9niDgCeq19gdj4E1z. Yours won't be that, but something similar. That is the key that you should copy to your PC, not "passkey". When integrating MAC and PCs you have to use the actual code, and not the "password" that you typed in. You will find it here:
1. Open Airport Utility
2. <click> Manual Setup
3. <look top tabs> <click> Base Station
4. <click> Equivalent Network Password
5. You will see two types of alphanumeric codes: ASCII and HEX. I use the ASCII, but if that doesn't work, you might try the other. Unfortunately you can't copy and paste from there, so you will have to do a screen shot, or copy the number out and type into your PC.