The 802.11b specification defines only 40-bit WEP. All implementations of 128-bit WEP are therefore vendor-specific. This affects encryption between Cisco and third-party wireless devices.
If a non-Cisco device uses the same algorithm as the Cisco device, then a WEP-protected connection should be possible. Each vendor uses their own algorithm for 128-bit encryption. Cisco equipment uses 26 hexadecimal characters for the 128-bit WEP key.
If the non-Cisco card uses ASCII, you may need to convert to a hexadecimal value or vice-versa. However, since 128-bit Wired Equivalent Privacy (WEP) keys are not tested (40-bit keys are tested for compliance) by Wireless Ethernet Compatibility Alliance (WECA) for Wi-Fi compliance, there is no guarantee of interoperability.