Ask YC: Javascript, memory usage

Is there a rough rule of thumb for what's a reasonable amount of memory for your Javascript to be using? My worst case scenario is a six year old laptop with running XP / IE6.

On a related note, any recommendations for how to avoid memory leaks in Javascript? I understand how they occur but was wondering if anyone was using any frameworks and had any best practices to keep them from forgetting to unhook event handlers and whatnot.