[freeza]

It's the "Activesync" folder in \Windows

As for your other issues....
-It shouldn't slow down when browsing the Windows folder per-say.. Initial loading of the Windows folder will be slow, and subfolders will also load slow but browsing should not be slow at all.
-You can delete Sprint Navigation from \Program Files as well as the links, located in \Windows\Start Menu\Programs.
-Making the Sprint Navigation tab in Manila work with TeleNav will not work, UNLESS you make the folder structure of TeleNav identical to that of Sprint Navigation. This means that you will have to copy the Sprint Navigation folder in \Program Files to your computer as well as the TeleNav folder and mimic the folder/file structure of Sprint Navigation, then delete Sprint Navigation from \Program Files, and copy TeleNav in its place. (if that makes sense) NOTE: this is only a guess, it may or may not work but is worth a try if you want the Sprint Navigation in Manila to work with TeleNav.

Post results if you decide to try!