Well, vst plug-ins require a "host" -- they don't run by themselves, they require another program to host them in. Most editor & multitracker type thingies will support vst plug ins.
VSTi's specifically, are VST instruments. Normally I use this little host right here:http://www.hermannseib.com/english/savihost.htm
You don't even have to have a Midi keyboard to use them. The SAVIhost has a virtual keyboard you can click with your mouse... OR, your actual keyboard
keyboard -- the one with letters on it..is actually playable & provides up to 3 octaves!
4 rows of keys-- the very bottom row, the ZXC line, has the white keys of the lower octave, the ASD line right above that, has the black keys for the lower octave. the QWERTY line of keys is the white upper octave, and the black keys for the upper octave are on the line of numbers.
Pressing SHIFT will drop you down an octave.
Same guy that made the savi-host, also made the vsthost:http://www.hermannseib.com/english/vsthost.htm
You can do the same with you keyboard or mouse & an instrument... but also, wit vsthost you can add effect plug ins.
As for the effects, I use these mostly:http://www.kjaerhusaudio.com/classic-series.php
Okay, I am gonna gve up my main source for freebie audio! LOADS of vst instruments, effects, et cetera, many of them free, can be found here:http://www.kvraudio.com/
Up at the top right, it says "quick links are hidden. click here to view them" -- then you can choose to search by name, for an instrument, an effect, a host...
But each program has a line that tells you what PRIMARY TYPE of software it is...which is a LINK. Like this page:http://www.kvraudio.com/get/126.html
ahhhh yes, the "Organ one", found alphabetically.
You may not like this particular organ-- but you DO want an organ sound. Just click "organ" where it says "primary type: organ". You get a list of EVERY type of organ kvraudio has listed-- telling you whether it is free or not. You just click around until you find a much much cooler free organ -- like THIS one, the PHIBES:http://www.kvraudio.com/get/314.html