It likely depends on what you are looking for in a book, based on your own specific needs or wants. If you desire a basic manual, for example, try "The 9mm Walther P38 Pistol" handbook, available at Midway at this link:
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=865345
I've got a copy of this one; it's both inexpensive and quite handy.
If you are looking for an owner's manual, D.R. Morse's "Walther P-38 9mm Auto Pistol Owners Manual" is offered here:
http://www.rayrilingarmsbooks.com/cgi-bin/rrb455.cgi/4865
An assembly/disassembly manual for the P38 by Skennerton & Riling can be found here:
http://www.amazon.com/Walther-Assembly-Disassembly-Manual-ILLUSTRATED/dp/0949749702
Maj. George Nonte's "Walther P38 Pistol," which provides history, development, and technical data, as well as material on assembly/disassembly, can be found here:
http://www.booktrail.com/Guns_Handguns/Walther P-38 Pistol.asp
If you want to sort through a number of other selections, try this link to a variety of books devoted to the P38 and select the one or two that seem best for your needs:
http://www.google.com/products?sour...R:2005-49,GGLR:en&q=books+on+walther+p38&um=1
By the way, a sticky notice on the P38 Forum advises gun enthusiasts to buy books
before they buy guns. It's generally good advice. The data contained on P38s on this particular forum is a treasure trove for collectors, owners, and enthusiasts alike. You can find it at:
http://www.p38forum.com/
Good luck.
