Nope they're completely different products.
If you take a look through the colour collections thread which includes the mineralized loose foundation, there are quite a few posts in there which highlight the differences.
MSFN is not a foundation (though some may use it as that). The coverage is really quite low, though it is definately buildable in my opinion. Mineralized Loose IS a foundation- it has way more coverage than MSFN.
In my opinion, MSFN are also somewhat more 'glowy' than the Mineralized Loose, though I have heard others say differently.
Light Medium MSFN is a different shade to Medium- I suppose it is lighter. It's different though- it has more yellow tones in it, whereas I find that Medium is very beigey. On the other hand, if you were considering Mineralized loose... the 'Light' shade is as dark as Light Medium MSFN and, in comparison to Medium MSFN, is definately much more yellow toned!
I'm not really sure what shade of the mineralized loose you would be- it would probably be best to try it out in the store if possible. I am NW15 and I have 'Light', which is much darker than the Light MSFN (and a bit too dark for me), so perhaps you would be a Light Medium?