I've had some Sony orchestral loops dormant on my pc for a while,and I was just perusing through them,and realized that a few would sound pretty good on a song I'm working on.
However ALL of them are in major keys,and thus don't quite work with my song which has a lot of minor chords.
I don't quite understand the principal of using loops,because apart from changing the key which is simple enough or really mangling them up,or using them for hiphop/dance riffs,what happens if I need a B minor or diminished chord for example,but the loop I like is B Major?
I can get away with some of the bass loops (as they play mostly the root note)and obviously drums.
This has always baffled me.
Is it just pot luck when it comes to this kind of loop, and you've just got to hope that a particular one you like matches your project,or is there a way of manipulating individual notes like with midi?

Part luck, part manipulation. melodyne is one way to go about it.  V-vocal may give you some results.  Your post ironically is a reminder to those that think working with loops is easy that other thanb the most basic usage, it requires work.  You hit the nail on the head when you mentioned really mangling them up.  When yo9u look at the world of loop production, you are talking about guys who produce basslines through weird methods like re-sampling 808 kicks and pitch- shifting them to be melodic.  mangling is the name of the game.

IF they are acid loops they should follow the tempo and key changes.  Doesn't mean they will work (or sound good, anyway).  That is the trick w/ loops - finding the one's that work w/ your song.

@

Using loop explorer in x1 has many beifits including pitch.
turn pitch on and change the relitive pitch to C.
this way if you want to change the key of your loops later on you will be able to at leat match the key.

you might find propellerheads recycle the most helpful because it allows you to make rex files,rex are loops but have info in them like tempo and pitch.

Lampoon land - that's a great question.  I'm reading the responses with interest.

Changing a major sounding loop to fit a minor chord could be difficult unless you have got the polyphonic version of Melodyne. (assuming that all major chord tones are sounding at once. If they are not and the major chord is sequential then the standard version of Melodyne could be OK (or V Vocal of course) 

But there is another work around. Think of the major chord that fits a minor chord. eg F Major will work with a D minor chord for example.  D Minor has the notes D F A and D minor 7 would include C. But the F Major chord is embedded in there as well. So start with the root of the minor chord and go up a minor 3rd and try the major that is built on that note. 
It may not sound right but it could also work very well.

A C major chord may also work with D Minor because if the C major chord is built around C, E and G then C will work with the D Minor chord (minor 7th) but G will spell out a D Minor 11 sound and E will spell out a D Minor 9 sound and these may work well too. 

Try and see. F Major over a D minor chord is the first best option.

Thanks for all the responses.
Lawajava,it's just been one of those things that has always perplexed me somewhat
I don't really write FX saturated songs,so I don't really need/want to mangle sound so much - maybe a few sound effects/loops here and there to add flavour.
I remember hearing the Robbie Williams song 'Millennium' (and  erased it from my memory banks immediately afterwards) At the time, I assumed a sample of the Nancy Sinatra song "You Only Live Twice" was used - but I later discovered it was re created by an orchestra(for cost reasons) - and I thought to myself,that could be useful if I wanted ,say,an orchestral section in a song.
    Now,some years later,I remembered that I had folders full of Sony orchestral loops(samples,loops,same principal) on my old PC;so I play a few,and to my delight discover that one or two might sound pretty good in my latest song.   
But oh dear,it aint gonna be quite so simple as I thought.....the damn things are all in major keys,and don't even come close to working in my arrangement.
Jeff,I tried your work around,but no joy.
  It seems to me, that apart from truly mangling the loops,the best way to use them would be to create a song AROUND the loop rather than fit them into an already structured/finished arrangement. 
I don't have Melodyne,but I have a feeling that the aforementioned samples I have might be too complex to get any satisfactory results with it.
In many cases,it's down to luck as to whether they're going to fit *shrugs*