The 4800 had two models. The 4800, and the 4800b. If you have a B model is it identical to the Cisco 340 series. If you have the orgional 4800 model, it is NOT the same as the Cisco 340. An easy way to tell the difference. Is there a green power switch on the Access Point? If YES, this is the older 4800 model. If no, then it is the 4800B and the same as a 340.
If you have a 4800- It does not use the same code as the 340 or 350. It has a different operating systems. The latest code is 8.55.
Improving singal quailty- First of all make sure you have the latest firmware, drivers and utilities. There were some changes made over time to improve these. The best method to use for link quality is to view retry counts. Signal strength can be very low, yet the RF link can work fine, adn in other cases (multipath for instance) signal strength cna be high and the overl link is poor. Retry counts is the best method to determine the link performance.
The AP4800 does NOT support LEAP or EAP. Not all 4800s supportes 128 bit WEP either. You will need to check if you client card support 128. If it does, it shold work fine with LEAP if the AP is a 340 or 350.