Coming early in 2007. Cobb is very respected in the Subaru community. Looking forward to what the come out with and what gains it might provide:

http://www.iaperformance.com/product_info.php/products_id/2357

"Nissan: 350Z, Titan, Armada, Altima, Maxima, Xterra, Murano, Sentra (est 1st quarter 2007)"

Actually, I think they are still looking for an xterra owner to allow them to use their truck for tuning. I know they were looking, but I don't know if anyone ever stepped up.

Yes the Cobb unit for a Titan is due to be release sometime 1st Q 07 but nothing have been mention about an Xterra yet.
www.cobbforums.com