Namaste Padipa,
thanks for the post.
well.. this is a very interesting topic, to be sure
within the context of Buddhism, yoga is viewed in several different ways, depending on ones' Vehicle and school. as such, the Theravedans, by and large, view yoga is exercise and physical conditioning, which has its own value, but there isn't much of a spiritual aspect to it.
this would be analgous to Hatha Yoga which is, for the most part, a yoga of phyiscal exericse... and exoteric yoga.
yoga comes from the Sanskrit root "yug" which means to re-join or re-link. in the understanding of India, this is a re-joining or re-linking of the mundane aspects of self or conciousness (depending on your view) with the supramundane aspects.
within the Vajrayana, however, yoga is viewed in a different manner. whilst there is some Hatha yoga, the general focus is on the other types of yoga, the more esoteric aspects, if you will.
depending on ones individual lineage within the Vajrayana, the yoga practices have somewhat different names, however, all schools of the Vajrayana generally practice the same yogic praxis, with some variation due to individual capacities and so forth.
however... rather than rambling on, let me cut and paste something from the forum which i've contributed before:
here's a link to a Tantric teaching:
http://www.comparative-religion.com/forum/showthread.php?t=2240
here's a link for an explanation of Tantra from the Buddhist point of view:
http://www.comparative-religion.com/forum/showthread.php?t=904
Tantra means thread in Sanskrit, specifically the warp thread that dresses the loom and gives support to the fabric formed by the moving shuttle or, in a rug, the individual knots. Without it, there can be no cloth. It can also refer to the cord used for stringing beads to make a necklace, a rosary, mala, or garland. Tantric or more rarely, tantrik, is the adjective.
The word "tantra" refers to an "oral practice tradition," where there is a direct link from teacher to student. It is important to understand that a tantric connection is more than a lineage association, or an affiliation to a tradition. To belong to a certain tantric lineage means that the skills themselves are learned, practiced, mastered, and handed on with a special kind of permission.