DOPAMINE != HAPPINESS
I cannot emphasize this enough! There are around a dozen different pathways of dopamine-using neurons in the brain; while a number of these seem to be involved in some sort of expectation/reward system, a number are not. Even in this reward system, it's a far cry from dopamine=pleasure -- there's a relation between the function of dopaminergic neurons and expectation/learning of reward, but it's not nearly that simple.
Now, the corpus striatum refers to a portion of the limbic system of the brain, mainly the caudate and putamen. Two of the most-studied (and prob important) pathways of dopamine-using neurons converge on the corpus striatum. First, neurons from the substantia nigra, involved mainly in motor movements (this is what quale was talking about) connect to the dorsal (towards the back) parts of the striatum. Neurons from the VTA, involved in expectation/reward/learning (these are the fun ones) connect to the ventral (forward) parts of the striatum, especially the nucleus accumbens. So your drug could be acting on both these systems.
The D2 receptor is indeed intimately involved in the reward functions and is the subject of much study.
There seems to be a misconception that amphetamine doesn't block transmitter reuptake; it does. In fact chemicals that induce release and enter the cell via the reuptake transporter block reuptake to some extent, merely by competition for transporter sites. This is probably the only way in which amphetamine blocks reuptake. [1] contains a detailed discussion of this.
The primary mechanism of action of amphetamine is its direct stimulation of NE and DA release, probably by reversing the reuptake transporter, the same way MDMA works. This is called "carrier-mediated reverse transport." Amphetamine is active as a serotonin releaser, but is very weak. The effective concentrations are below[2].
NE release: 7 +/-1 nM
DA release: 25 +/-4 nM
SE release: 1750 +/-100 nM
[1] Seiden LS, Sabol KE, Ricaurte GA. (1993) Amphetamine: effects on catecholamine systems and behavior. Annu Rev Pharmacol Toxicol 33:639-677.
[2] Rothman RB et al. (2001) Amphetamine-type CNS stimulants release NE more potently than they release DA and SE. Synapse 39:32-41.