Since the laptop isn't yours but is your employer's, you don't have leave to install software unless it's approved by said employer, and even then said employer would probably prefer that any such installation be done by IT personnel.
You would be well advised to spend a few hours doing internet research on the subject of getting a USB drive to boot. If the stick can boot, so should a hard drive.
Having said that, if you still intend to install software and risk losing the privilege of using that laptop (and possibly your employment) then use winxp software to make a partition in which to install ubuntu. When you install Ubuntu, select that partition as the one to install into. Be carefull when you reach to stage of configuration of the bootloader. Watch for an option to install Ubuntu's bootloader into the root partition, and not to the MBR. Then, when installation is complete, reboot into windows and configure Bootmagic to add Ubuntu to the Bootmagic menu.
If it turns out that Ubuntu didn't have an option to install it's bootloader to the root partition, all is not lost. When you reboot, select windows from the Ubuntu boot menu. When windows is running, start bootmagic and look in the configuration options. You should be able to restore Bootmagic to the MBR quite easily.
If, in your attempt to install Ubuntu you happen to install over one of the windows partitions, I hope you have a backup of said partition that you can restore (such backups should be the norm before meddling with partitions anyhow). Otherwise, you will have some explaining to do at work.