Yes you can use BoxCryptor on both computers. The BoxCryptor folder which is located within your SkyDrive folder is automatically synchronized with the SkyDrive client. So BoxCryptor encrypts and decrypts your files from the BoxCryptor folder and SkyDrive synchonizes the encrypted files which are located in the BoxCryptor folder.
Multiple drives do not mean multiple computers. Multiple drives mean that you can use more than one BoxCryptor folder at the same time.
Regarding licensing: If you use BoxCryptor for any business related data you always have to purchase BoxCryptor Unlimited Business!
To use more than one BoxCryptor drive at the same time you also have to purchase BoxCryptor Unlimited which provides multiple drives.