They are the same. The confusion comes from the way different manufacturers interpret the WEP specification. WEP actually has two parts, a "secret key" (user settable), and a 24 bit "Initialization Vector" which is not under user control.

Some manufacturers specify the length of the "secret key", i.e. user programmable, part of the WEP key, and others use the "secret key" plus "initialization vector" length. Curiously, this confusion is only seen on the lowest level, i.e. 40/64 bit, of WEP... probably for historical reasons.

Since all 802.11 products now support 128bit (and sometimes higher) levels of WEP, this problem is moot. If you enable WEP, you should always use the highest bit length available, since there's no performance penalty from using the higher number of bits.