If you want to boot an unsupported operating system (e.g. Windows 95), chain-load a boot loader for the operating system. Normally, the boot loader is embedded in the boot sector of the partition on which the operating system is installed.
grub> rootnoverify (hd0,0)
grub> chainloader +1
`+1' indicates that GRUB should read one sector from the start of the partition. The complete description about this syntax can be found in Block list syntax.
However, DOS and Windows have some deficiencies, so you might have to use more complicated instructions. See DOS/Windows, for more information.
 This is not necessary for most of the modern operating systems.