I'm new to Ubuntu and just installed it on my HP Compaq nx5000. I dual-boot installed with Windows XP. When I boot, it goes to the grub bootloader. At the bottom of the Grub list it says boot Windows XP professional. But when I select the last one and press enter, no matter how many times I try, it either loads Ubuntu or goes back to the bootloader.
Use Boot-Repair, Boot-Repair is a one-click solution that detects currently installed operating systems and updates grub configuration.
On Ubuntu open up the Terminal (if you don't know how, open the Dash launcher and type terminal). In the terminal window type this in:
It will ask for your user password (the one you use to login to Ubuntu). Type it in and press enter. After that some text will come up in the terminal (it should be pretty similar to the text you get on the grub boot menu screen). After a minute, when the command stops restart and try loading Windows XP again. Tell us if it works.