glass said:
As I understand it (and I must admit I haven't actually read any of the novels), Smersh was the organisation from all the novels, and was just soviet intelligence. SPECTRE was created for the films to replace Smersh, for whatever reason.
Both organizations were mentioned in the books, but SMERSH was used more often than SPECTRE, actually. SMERSH (as Nuclear Platypus mentions) was based on the real SMERSH organization, while SPECTRE was a wholly unique creation (although there were some controversies over who created it, part of what led to the whole Thunderball rights dispute).
SPECTRE was Blofeld's organization, and only appeared in a couple of novels- Dr. No and Thunderball were the only ones, I believe. SMERSH, on the other hand, appeared in several- Casino Royale, From Russia With Love, and... well, I can't remember what other ones, but a few more.
In the movies, they did switch from SMERSH to SPECTRE- I'm not sure of the rationale behind it, I seem to vaguely recall that it had something to do with the use of a "real" organization's name, but I'm not sure. There are still a few references to SMERSH in a couple of early Bond flicks, all the same (the one I remember offhand is in From Russia With Love, when Bond at first thinks the villain might be with SMERSH, but he turns out to be with SPECTRE).