Haynes recently came out with a repair manual for Subaru's from 2000 to 2006. I've used them on other cars and found them very resourceful. There is also a Chilton manual, but haven't used that one. Here is the link to buy it at:

http://www.themotorbookstore.com/15639256199.html

Is there one that covers a 98 Impreza? Chilton makes one that goes up to 96 and Haynes now has this one that starts at 2000.

 

Is there enough difference between my 98 Impreza and a 96 that I need to worry about getting the new manual?

You should be seeing them now at most local auto parts stores - don't have to pay for shipping.

 

Still waiting for a dedicated 2005+ maunual for the turbos....

While I have either haynes or chilton manuals for general stuff. I wouldn't trust them as far as a fetus could throw them for wiring and critical information. FSM is the only way to go for that stuff.