Those piperazines used as de-worming agents can't cross the blood brain barrier in to the brain, which therefore means that they don't have any psychoactive effect.
All of the piperazines exhibit some level of toxicity (which is part of what can give people the nasty hangovers), and it's this toxicity, combined with a paralysing effect, that gets rid of worms in the gut. As the worms are much smaller than the animal being dosed, the worms get a much higher dose in proportion to their size, which kills and/or paralyses them. The commonly used psychoactive piperazines also have this effect lol, but you would probably die of crazy over-stimulation before the dose was high enough to kill any worms.
The main psychoactive piperazines that are interesting and that you would ever stand half a chance of getting are as follows:
BZP - The most common, stimulating, and amphetamine-like recreational piperazine, alot of people's favourite.
MBZP - Slightly less potent, and apparently less toxic, derivative of BZP which is used as a 'better' alternative to circumvent BZP bans.
TFMPP - A mildly hallucinogenic and fairly inert piperazine alone, which however is used to mix with BZP and boosts the overall effect quite greatly.
pFPP - Another mildly hallucinogenic piperazine which is said to be slightly relaxing, I have heard good things about this one.
MeOPP - Another piperazine which is said to induce comparatively much less anxiety than its counterparts, and again even to be relaxing instead of stimulating, although I have doubts about this one.
2C-B-BZP - Basically a stimulant similar to BZP but not quite as nice, unfortunately does not produce effects similar to 2C-B.
mCPP - A pretty nasty one that basically just induces massive migraine headaches lol but still manages to creep its way in to some street pills somehow.
MDBZP - When developed was expected to have activity similar to MDMA, but ended up effectively producing all of the negative effects of piperazines without any of the positives.
DBZP - A by-product of BZP manufacture that indicates a poor quality product, which is not known to, but could, have stimulant effects.
There are other, much less known of ones, but they are generally just as, and most likely more, toxic and generally crap lol.
There are threads around that discuss most of these above piperazines individually, and there's always Google, but yea, it's interesting stuff, hope it helped