Ok Nissan just released the 05-06 Xterra Seat Covers for the Xterra,
there is 3 options,

Fold Flat Front Seat
Fixed Back Front Seat
Rear Seats

These are the water resistant Genuine Nissan Covers, they come in Gray and Black and have the Xterra Name on the Headrests, Very nice product..

http://www.yournissanparts.com/catalog.aspx?StoreName=nissanofturnersville&DeptID=191674&page=2

Check em out!