If the keyboard has midi out capabilities, then yes, you can use it as a controller for a sampler.
If your interested in software sampling devices, I'm sure you'll find one here... http://www.kvr audio.com/get.php?mode=...&sort=1&rpp=100
BTW, 30 or so of these are freeware..
Your question about the difference is very broad. There are many types of synths. Generally, they work by using preloaded samples ( workstations ) and / or generating electric tone waves ( Analog- sine, square, etc ). This is very basic info though.. There are many types of synthesis. Go have a look at KVR audio and click on "Instruments". You'll see what I mean... and those are just software synths.
A sampler is a piece of equipment that allows the user to record his / her own samples and then play them back via a midi controller ( often a keyboard ) or sequencer. Several synths and workstations include sampling facilities as well.
There are many sites that can answer this more fully ( and a lot better ). I would suggest a search in google. There are also plenty of good links at the Synthzone homepage.
[This message has been edited by Bluezplayer (edited 01-18-2005).]