No, you cannot - using either iSync, .Mac Sync or the Backup application available to .Mac registered users.
iSync synchronizes only Calendars and Contacts, with mobile handsets and Palm handheld organizers or smartphones.
.Mac Sync synchronizes only Bookmarks, Calendars, Contacts, Keychains,
Mail Accounts and Mail Rules, Signatures and Smart Mailboxes with other Macintosh desktop and portable computers through .Mac, and with the .Mac servers themselves.
Backup will back up and restore your iTunes library to and from .Mac, external hard drives or removable media, but will not synchronize your library.
You are really asking the question in the wrong forum. You should consider posting your message in of the subcategories of the iTunes forum, here:
http://discussions.apple.com/category.jspa?categoryID=149
You could use an application like ChronoSync to synchronize your libraries, but you are liable to get the best advice about iTunes synchronization in the iTunes discussion areas. More information about ChronoSync is available here:
http://www.econtechnologies.com/site/Pages/ChronoSync/chrono_overview.html
