Basic or comprehensive?

For basic, Chilton 64304  works fairly well. See your bookseller. They
may have to order it.

If you want more detail, the factory manual(s) are available online as
fee-paid downloads at http://techinfo.subaru.com/html/index.jsp

Some enterprising souls have compiled the downloads onto CD and are
selling them on eBay.
http://cgi.ebay.com/ebaymotors/SUBARU-FORESTER-SERVICE-REPAIR-WORKSHOP-MANUAL_W0
QQcmdZViewItemQQcategoryZ6762QQihZ018QQitemZ280075405327QQrdZ1
http://cgi.ebay.com/ebaymotors/1999-2004-Subaru-Forester-Factory-Service-Manual-
CD-03_W0QQcmdZViewItemQQcategoryZ34223QQihZ019QQitemZ290078274699QQrdZ1