Hello!
In this tutorial I show you how to cross compile altcoin-qt using mxe and mingw.
What is mxe? Well this is set of makefiles allowing you compile an cross environment with needed packages (mingw-w64, qt, boost, etc) without pain.

For example I will compile blackcoin-qt for 32-bit Windows on 64-bit Ubuntu 14.04 LTS, but this method should work with another altcoins.

Step 1.
Firstly we need install cross compile environment.

Install mxe dependencies:

For 64-bit Ubuntu also install:

Step 2.

Clone mxe github repo (if you just download zip archive from guthub, mxe may not work):

Our environment will be placed in /mnt/mxe

Step 3.
Now we need compile boost and qt5 for our environment (need a couple of hours for this).
If you compile something using mxe and move mxe directory to another place, then mxe will not work because all what you compile linked statically
Compiling boost will fail if memory of your PC less then 2GB. Making swap partition will fix this.

Compile boost:

Compile qt5:

If you need qt4 (for some altcoins):

mxe automatically determine all dependencies and compile it.

Step 4.
Unfortunately mxe not support berkeley db and miniupnpc so we need compile them manually.

Compiling berkley db:
Download and unpack berkeley db:

Make bash script for compilation:

Content of compile-db.sh:

Compile:

Compiling miniupnpc:
Download and unpack miniupnpc:

Make bash script for compilation:

Content of compile-m.sh:

Compile:

Step 5.
Yay! Making our environment is done! Now we can compile blackcoin.

Add mxe bins to PATH:

Download and unpack blackcoin sources:

Make bash script for compilation:

Content of compile-blk.sh:

Compile:

And that all.
Our blackcoin-qt.exe placed in /mnt/blackcoin/release
Hope this help someone