Partitions filesystem (partsfs) kernel module.
PartsFS allows mounting a disk image as a filesystem.

Compile:

$ make

Simple, isn't it? :-)

Usage (as root):

$ insmod partfs.ko
$ mount -o loop -t partsfs DISK_IMAGE TARGET_DIRECTORY

Example:

$ fdisk -l freedos-img/c.img 

Disk c.img: 10 MB, 10653696 bytes
4 heads, 17 sectors/track, 306 cylinders, total 20808 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xe3657373

Device Boot      Start         End      Blocks   Id  System
c.img1   *          17       20484       10234    1  FAT12

$ mount -o loop -t partsfs freedos-img/c.img t

$ ls -laih t
      1 drwx------  2 root    root       0 2012-01-06 17:19 .
3014683 drwx------ 15 andreax andreax 4.0K 2012-01-06 17:18 ..
    101 -rw-------  1 root    root     10M 2012-01-06 17:19 1

$ df t
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/loop0               10404     10404         0 100% /home/andreax/partsfs/t

$ file t/1
t/1: x86 boot sector, code offset 0x4c, sectors/cluster 8, root entries 512, sectors 20519 (volumes <=32 MB) , Media descriptor 0xf8, sectors/FAT 11, heads 4, hidden sectors 17, serial number 0x0, label: "           ", FAT (12 bit)