It does a lot of things such as icon building and as such can take a very long time. Some machines will have "add-ins" that explorer will call to render the icon and this will vary from machine to machine. There is no cure.
If I want to go fast, I use Gyula's Navigator which is a true file and directory browser which Explorer is not.
Your issue is a common complaint is best answered that its a matter of education that Explorer is not a file browser.
One of our local workstations-lan connected, has begun to take excessively long time to highlight / open some folders. ( Have view tools set to - single click, underline when pointed @) similar folders in same directory highlight and will open instantly-but the offenders will sometimes take many seconds to highlight or open- if I hover on top of folder icon-right click-open the action is near instant but if I close and come back to hover, the time lag is still there. tried clearing prefetch, tried editing registry for different prefetcher #'s (1-2-3-) tried creating new folder-copy all contents and delete old one, not much difference, copied entire partition contents to new partition..other computers show no inclination to do this-stations are all Intel D865 mainboards-P4 2.6's to 3.0's. tried disconnecting completely from lan, chkdisk-defrag, etc.. any ideas (2 Hd's, 5 partitions- C kept primarily for OS and programs-others for data and shares-etc) TIA