Doping for Dummies

Here is a good generalization of what and how for the basics.

http://www.roadcycling.com/cgi-bin/artman/exec/view.cgi/4/853

R-EPO is injected to cause the body to produce more red blood cells which are what carries oxygen in the blood. These concentrations of red blood cells can get up to the 50% allowed by the UCI, this 50 being the hematocrit level. The UCI came up with this number because it is a generous top level, most elite athletes usually being in the low-mid 40s. Since R-EPO has become more well known by doctors as to how to use it it has become much safer. In the early days of athletes self-medicating they would end up with with hematocrits that were so high that there blood would thicken to the point that they would get a clot and die if they didn't move for an extended time. The most prevalent of these is when they were asleep.

Blood transfusions are done for the same reason but instead of adding a drug, new red blood cells are added directly to the blood stream. These are obtained from either a donor or the athlete themselves having blood drawn which is then spun in a centrifuge to seperate the red cells from the white and the plasma. This method results in a lower hematocrit level than what could be obtained with R-EPO but is usually safer and is often harder to detect if the blood was taken from the athlete originally.

Testosterone is the same as the anabolics that are used in most other sports. They use it to build strength and for the possible endurance gains that can come with increased testosterone.

Anything else you wanted to know, such as testing procedures can probably be found in the article.