From this Knowlegebase Article:
If you want to join a non-Apple encrypted wireless network from a computer with an AirPort card, you must use one of two different styles for password entry; and it must be the one chosen by the network administrator. They are:
1. ASCII password
If you were given a password that may be plain language, containing characters from the full range of ASCII, use the double quotation mark (") before and after the password. These are case-sensitive, and they are five characters long for 40-bit encrypted networks or 13 characters long for 128-bit encrypted networks.
Example of 40-bit: "pw123"
Example of 128-bit: "password12345"
2. Hexadecimal password
If you were given a password that uses only the hexadecimal range of characters (which are: abcdef0123456789), put a dollar sign ($) before the password. These passwords are 10 characters long for 40-bit encrypted networks or 26 characters long for 128-bit encrypted networks. In a hexadecimal password, the dollar sign is called the Hex Escape. It notifies the software that the characters that follow it should be treated as a hexadecimal number. Other possible hex escapes are "0x" and "0X" (zero-x, and the "x" may be upper or lower case).
Example of 40-bit: $1234abcdef
Example of 128-bit: $12345678901234567890abcdef
If you want to join a non-Apple encrypted wireless network from a computer with an AirPort card, you must use one of two different styles for password entry; and it must be the one chosen by the network administrator. They are:
1. ASCII password
If you were given a password that may be plain language, containing characters from the full range of ASCII, use the double quotation mark (") before and after the password. These are case-sensitive, and they are five characters long for 40-bit encrypted networks or 13 characters long for 128-bit encrypted networks.
Example of 40-bit: "pw123"
Example of 128-bit: "password12345"
2. Hexadecimal password
If you were given a password that uses only the hexadecimal range of characters (which are: abcdef0123456789), put a dollar sign ($) before the password. These passwords are 10 characters long for 40-bit encrypted networks or 26 characters long for 128-bit encrypted networks. In a hexadecimal password, the dollar sign is called the Hex Escape. It notifies the software that the characters that follow it should be treated as a hexadecimal number. Other possible hex escapes are "0x" and "0X" (zero-x, and the "x" may be upper or lower case).
Example of 40-bit: $1234abcdef
Example of 128-bit: $12345678901234567890abcdef