hmm.. this is a little troublesome.. as the easiest way of going about is installing xp, then 7 and then ubuntu..the problem with windows bootloader whether xp or 7 is that it does not provide a choice of where the bootloader is to be stored. this option being available in the grubloader, it doesnt overwrite the previous windows bootrecord. hence, after installing ubuntu, the previous boot entries for the windows remain in place..
now the problem is, ubuntu will need its grubloader. and to rewrite the grubloader, you will have to boot into ubuntu from a live cd or usb pendrive, and then use the terminal command line to restore the grubloader and then edit the grubloader to include the entries of windows xp and windows 7.
i recently installed ubuntu a few days back.. what i did was write the bootloader in a separate location than the windows 7 loader, so now instead of using the grubloader to boot into windows, what i have is first the grubloader screen, from there if i choose windows 7, i go to the windows 7 bootloader screen, and from there i can easily choose between windows 8 and windows 7. but now i have removed windows 8.
so basically, i have both the bootloaders.. installing ubuntu or linux after windows is always the easier option as the grubloader will support loading of a wide variety of operating systems whereas the windows loader will not.