First, I am assuming that you are familiar with the backing of your selected wallpaper and that it is a non-PVC backed wallpaper.
To learn more about sustainable wall finish options, see the GreenHomeGuide post "What green options are there for wall coverings other than paint?" by Marian Keeler.
To answer your specific question:
- you want to focus your search on cellulose paste adhesives such as Ecofix P7 by Roos International or Roman Decorating Products.
- And remember to look for Green Guard certification on any adhesive product.
Lastly, you can make your own wallpaper paste -- here is a handy low-VOC recipe from Care2.com.