I believe that speed is an issue when you connect an 802.11b device to an 11g network but I'm not familiar with 11a (which I guess means it's older and slower than b -- so draw your own conclusions)
Given the low prices of wireless adapters why bother ? Presumably you also want the security of using WPA encryption, so upgrade ?
You are about to answer a thread that has been inactive for more than 6 months. If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.