As good as ActiveSync synchronize the standard Outlook features, it lacks support of sub-folders, public folders, etc.
Now you might get a solution: Chapura's PocketMirror Professional which was available for Palm based devices only in the past is also supporting Windows Mobile now and the only Outlook synchronization software that synchronize multiple Outlook Contacts, Calendars and Tasks folders with the corresponding Pocket Outlook applications on the handheld and synchronize Outlook folders and categories on your PC with corresponding categories on your Windows Mobile handheld or Smartphone.
PocketMirror Professional for Windows Mobile is built around the way you have already organized your important information in Outlook on your desktop. Items in multiple folders on the desktop get transferred to the handheld in tact and into folder-like categories, not just dispersed among the items' assigned categories.
Chapura PocketMirror is available from Handango for US$ 49,95 - a trial version isn't available yet.
Cheers ~ Arne