hedwards: The books were written after the series was conceived of and released. They were tie ins sort of the way that those Star Trek and Star Wars books were tie ins.
The books weren't tie-ins, they were an alternative Red Dwarf.
Infinity Welcomes Careful Drivers starts off with Lister joining the Jupiter Mining Corporation and then does the whole Lister in stasis whilst the crew are killed by a reactor failure.
So far, so good, but from there on it separates from the TV series. There are similarities, yes, such as a second Rimmer hologram (but done by using the Nova 5's hologram generator and not the way it happened in the series - Confidence and Paranoia) and finding Kryten, but then there are very big differences too, such as using the Nova 5 to get back to Earth, but then that entire event turning out to be Better Than Life.
The second book, Better Than Life, is much the same kind of thing with similarities to plot events in the series, but done differently. For instance, Lister is dead at one point, and his body sent to Backwards world, which causes him to return to life. He lives there for thirty years (he is elderly and lives with an elderly Kochanski) and then when thirty years have passed and he is younger again his crewmates return for him.
As for Last Human and Backwards, they are two alternative sequels to Better Than Life.
So yes, the books are an alternative, and yes I really enjoyed reading them. :)