hi 2009novice,
i dun know much on buddhism, but i'd like to contribute.
Firstly, be careful of what books you read. Many books
misrepresent Buddhism, especially with regard to the Tibetan
Buddhism ( which is mainly referring to the Vajrayana vehicle of
practice).
In general, the reason why Vajrayana is considered esoteric and
had to be kept under wraps is to protect people in general from
getting wrong ideas about the practice. When people get wrong
ideas and then they start to slander Vajrayana, they commit a very
negative karma which harms themselves. So it is for this
reason that Vajrayana has to be more secretive and also to be
considered esoteric.
The question you have is exactly one of the sore areas that is
often misunderstood. In Buddhism, our main aim is to remove
the afflictions such as desire, hatred and ignorance. To do
that, there are several approaches:
In the Hinayana, desire is removed by avoidance. Meaning
desire is removed through contemplating the filthiness of the
human body to generate disgust and contemplating the negative
results from desire.
In the Mahayana, desire is transformed through mind-training on
compassion. Meaning, if one feels desire, one can pray and aspire
that by feeling desire and suffering from its ill-effects, one will
be able to take on the sufferings of all beings and relieve them
from needing to go through similar sufferings.
In the Vajrayana, desire is not avoided or transformed as in the
Hinayana and Mahayana but is instead utilised in the
practice. Just as poison is eaten by a peacock to make its
feather colors brighter and more brilliant. At this point, the
practitioner is very advanced.
At these high levels, the person needs to access a very subtle
level of mind to deepen his realisation of emptiness. He is
not like the ordinary person who is filled with desire. If you have
not reached such a level and not obtained permission from the guru,
to do such practices will almost be certain to fling you into hell
in your next life as it is a huge abuse of the Buddha's
teachings.
Sadly though, it seems that many people nowadays are trying very
hard to go to the hell realms