Ok, I've found someplace that maybe I can get some advice/help?  This is my situation and if anyone can give me advice I would be really thankful.  I work for a municipality and a position came open within the PD doing statistics and such.  I already work for the muni in another dept and have done minor work for the PD in the past so I was a natural fit.  I filled out my background investigation packet thinking thats as far as it would go, then I'm informed I have to take a VSA?  At first I had no idea what the officer was talking about.  Problem is, on my background packet for the response to marijuana usage I put that I had never used.  Well, wrong there was a period where I did use it, like 6 or 7 years ago.  Never sold it just was a casual user at the time.    The officer actually questioned me on if I had ever partaken of marijuana and I just said no but that I had been around it at parties.   Saying no was just a knee jerk reaction.  I had no idea I'd be interogated in this way.  Prospective LEA out there prolly have an idea that this treatment is coming but my background is in science and engineering.    Last weekend with my stomach tied up in knots I decided that this is so ridiculous that it isn't worth my stress and that I'm going to stick with my story and that the machine my say one thing but cannot prove anything.  This was my first time applying for a LE type position so I feel like a deer caught in headlights on this.  So do you agree that I should stick with my story and not give in?  I have heard that they can't technically disqualify you for failing a VSA?  I know that the department really wants to hire me after demonstarting my abilities in the past so could in some cases this almost be a formality that they must go through to hire someone?  Maybe they overlook some discrepencies.  I'm thankful I don't have to take a poly...that sounds far worse.  The detective told me just to stay calm and I'll be fine.  I'm so confused.

Thanks DeputyDog for your insight and help!  I take my test tommorrow morning and I'm trying to maintain a "don't give a shit attitiude" in my mind.  So, one more question if anyone can answer it.  There is no clear indication on the original city posting that you would have to take a CVSA or any type of "lie detection" test.  I went through and filled out my background packet only to have the VSA sprung on me at the end of the background interview.  No chance to try and work within acceptable limits(i.e. under 15 times marijuana, etc).  I'm just wondering if there are legal responsibilities to informing someone that they will be "tested" for employment before completing the background packet?  Seems like Officer positions usually have a statement about CVSA or polygraph right on the original posting whereas mine just indicated background check.  How was I to know what I was getting into?  Anyones help would be greatly appreciated.

Well I took the CVSA test this afternoon and from what I can tell everything went a-ok!  I was not interogated after the test at all.  I didn't want to ask if I passed for looking desperate or anything but they didn't have further questioning after the test and  stress levels looked "normal" according to him.   
This is the rundown of how I was tested for anyone out there that may care to know.  I was taken in to the office of the detective(for some reason I was half expecting to go to an interogation area, almost a padded cell situation with rubber hoses).  Sat down in a chair by his desk.  Had some small talk and joked around a bit.  He asked me if I was familiar at with all with CVSA and I played stupid about it.  Proceeded to inform me that the machine can detect inaudible stress flucuations in the vocal chords or something to that effect but basically that the machine can detect all lies( this I now know is BS thanks to this site) and I went along with it, at this point just wanting to get the damn test over with.  Gave me an attachable microphone and porceeded to ask me yes/no questions.    I got the marijuana question of course along with some other drug questions and criminal/stealing/abusing type questions.  I just answered with a straight face...not like I had a ton to hide other than the marijuana experimentation.  No print out or discussion/interogation afterward which I'm taking as a good sign!  Shook his hand and he said I'll see you around...oh, and to drive safe;)   So all in all I don't know how those machines can detect flucuations in voice patterns really unless you really had a seedy past and were nervous as a cut cat about being there in the first place.  Or if you actually  thought they worked and admitted to something during questioning.  I almost think its more a formality in some cases and as a way to get your voice on record maybe almost like a fingerprint.  And probably to intimidate others into confessing.  So now I wait again....guess they don't tell you if you pass or fail right there and then.  But I felt pretty good about the whole thing.  Thanks DepDog for your solid advice!