how do create the sfz file extension

In Notepad:
 
File -> New
Copy and paste the text line below, or simply type it in the same general format.
<region> sample=SAMPLE FILE NAME.wav oscillator=on
 
File -> Save As
Change the 'Save as type' to 'All Files'.
Type SAMPLE FILE NAME.sfz into the 'File Name' slot.
Click on the Save button, and navigate to Rapture's Multisamples folder.
Make sure that the referenced .wav (SAMPLE FILE NAME.wav) is in the same folder as SAMPLE FILE NAME.sfz
 
From Rapture, load the SAMPLE FILE NAME.sfz from the 'Load Multisamples' dialog.
 
It's a similar process in other text editors.  Effectively, you're taking a standard-issue .txt file (with proper opcode syntax that Rapture understands), and re-naming the file extension to .sfz.  Depending on your O/S and how it's set up, you may have to uncheck 'Hide extensions to known file types' in Control Panel -> Folder Options -> View -> Advanced Settings (or a similar path).
 

Cheers man, appreciated

I've done as you have said but fapture isn't recognising the sfz file

Done it now mate, typed the file name instead of what you said, thanks alot b rock, your a good man :)

When i load the sounds in they sound like they have a high/band pass filter on them

Three quick questions:
 
1).  Can you load the original 'raw' sample (.wav) into Rapture (Load Multisample dialog)?
2).  Have you checked the .sfz file for extra spaces, naming errors, etc.?
(You can copy your .sfz file text and paste it into a reply here.)
3).  Are you getting any error popups (sfzlog)?
(You can copy the error log contents and paste them into a reply here.)
 
EDIT:
I see that you've had some measure of success.  The end results will vary widely; depending on the original sample source, the length of the file, etc.  If this first experiment sounds like it has a HP / BP filter on it, look to the frequency distribution of the sample source.
 
Rapture is going to interpolate everything in the source sample, and 'reduce' it down to fit an oscillator's characteristics.  A .wav file of several seconds will get 'squeezed' into the space of a few thousand individual samples.
 
I don't know what you've used as a source file, but you can try some simpler .wav files, and build up to more complex ones.  Perhaps some single notes from a synth, or some drum hits.  You have to try a few dozens examples before you can get a 'feel' of what to expect in the results of a "forced oscillator".

it was samples from re-fills, they were a bit long, buzzing making wavetables though, i'm doing that just now, trying different sound sources, it's cool the zeta can generate wavetables, i should have a lot of fun programming, i've hit a brick wall with productions cause i'm not getting the sounds i want, hopefullyt  this will do the trick, it should do, cheers again. P.S as far as the three questions go, i typed the name fo the wave file instead of sample file name

Lucky.

typed the file name instead of what you said

Are you sure you should be allowed out with a loaded synth?