Crie uma partição estendida e crie partições lógicas. Eu não sei se o Windows 7 irá instalar em uma partição lógica embora
Explicação: (de Wikipedia - Particionamento de disco )
This section describes the master boot record (MBR) partitioning scheme, as used in DOS, Microsoft Windows and Linux among others on PC compatible computer systems. For examples of partitioning schemes used in other operating systems, see the general article on partition tables.
The total data storage space of a PC hard disk can be divided into at most four primary partitions, or alternatively three primary partitions and an extended partition. These partitions are described by 16-byte entries that constitute the Partition Table, located in the master boot record.
The partition type is identified by a 1-byte code found in its partition table entry. Some of these codes (such as 0x05 and 0x0F) may be used to indicate the presence of an extended partition. Most are used by an operating system's bootloader (that examines partition tables) to decide if a partition contains a file system that can be used to mount / access for reading or writing data.
Primary partition
A primary partition contains one file system. In DOS and earlier versions of Microsoft Windows systems, the system partition was required to be the first partition. More recent Windows operating systems (Win7, XP, etc.) can be located on any partition, but the boot files (bootmgr, ntldr, etc.) must be on a primary partition. However, other factors, such as a PC's BIOS (see Boot sequence on standard PC) may also impart specific requirements as to which partition must contain the primary OS.
The partition type code for a primary partition can either correspond to a file system contained within (e.g. 0x07 means either an NTFS or an OS/2 HPFS file system) or indicate that the partition has a special use (e.g. code 0x82 usually indicates a Linux swap partition). The FAT16 and FAT32 file systems have made use of a number of partition type codes due to the limits of various DOS and Windows OS versions. Though a Linux operating system may recognize a number of different file systems (ext4, ext3, ext2, ReiserFS, etc.), they have all consistently used the same partition type code: 0x83 (Linux native file system).
Extended partition
A hard disk may contain only one extended partition; the extended partition can be subdivided into multiple logical partitions. In DOS/Windows systems, each logical partition may then be assigned an additional drive letter.
Basicamente, você pode ter 4 partições "reais" em um disco; para obter mais, você cria até 3 partições primárias, depois uma partição "estendida" que tem várias partições "lógicas" dentro dela. A partição estendida NÃO obtém uma letra de unidade, mas as partições lógicas dentro dela receberiam letras se fossem designadas