The best way to do that is to create three partitions on the SSD, one for XP, one for Win 7, and one for Linux. Install the two versions of Windows first, then Linux. When Linux installs, GRUB will detect the Windows partitions and put them into the boot menu at startup, and you can choose which of the three operating systems you want to boot into.
You don’t want to install Windows after Linux, because it takes over the bootloader and you will lose access to Linux without having to resort to using an “Ultimate Bootdisk” on a USB drive or something like that. If you install Linux last, then GRUB will hand over the boot process to the Windows bootloader anytime you choose that OS.
Or, you can do what I did, and just install Windows and Linux on separate SSDs. I choose which one I want using the boot menu in the computer’s BIOS.