Modifying disk partition to free up a primary partition

On the hard disk as shown below, I'd like to
- change the type of the 4th partition
- create a primary partition for the free space
- install a different linux distribution on it
- keep the other two OS unchanged

Is it possible? If so, how?
Code:Model: ATA WDC WD5000LPVX-6 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags:

Number Start End Size Type File system Flags
1 1049kB 368MB 367MB primary ntfs
2 368MB 105GB 104GB primary ntfs
3 105GB 305GB 200GB primary ext4 boot
4 305GB 325GB 20,0GB primary linux-swap(v1)
-------------------------------------------------------------
175GB free space