[gentoo-user] Resizing a FAT partition?

Hi,

I have a SDcard of this layout:
Number  Start   End     Size    Type     File system  Flags
 1      4194kB  32.0GB  32.0GB  primary  fat32        lba

There are about 11 GByte of data on it.

The final result should be a SDcard with two partitions.
First a FAT32 with about 20GByte and a second with 10GByte
(ext4).

I took a look at parted and the resize command, which sounds
a little cryptic to me:

          resizepart partition end
                     Change the end position of partition.  Note that this does  not  modify  any
                     filesystem present in the partition.

One should use resize2f for that purpose.

Firstly I want to shrink the first partition and secondly it is a
plain FAT32 partition not ext-something. I did not find a 
"resizefat32" or similiar.

What tools do I need?
(beside the way to backup the SDcard, reinitialize it, put 2
partitions on it and copy back the stuff.)

How can I acchieve what I want?

Thank you very much in advance for any help!

Best regards,
Meino