Whenever I have installed Ubuntu, it has given me the option of if I would like to partition a disk and do an installation. I have never done it that way. Instead, I have a separate disk that I put Ubuntu on. The installation CD would show the two disks and ask which one I wanted to install on. I always had a smaller disk for Ubuntu, so identifying which one was easy. Ubuntu would do the rest, but it does make Ubuntu the default disk, and you will choose which disk you want to boot into using Linux's GRUB. You can, if you want, go into menu.lst and choose which operating system it will boot into after how many seconds have elapsed.
Ubuntu's programs can do everything the everyday user could hope to do: word processing, spreadsheets, image editing, slide shows, playing music and movies. There are games available for Linux, but not as exciting and graphically rich as those available for Windows. If you're a gamer, you won't like Linux. But for everything else, it will be a fun ride. GIMP is as close to Photoshop as you could wish, Inkscape does a nice job of doing tasks that Illustrator can do. For making brochures, books, and other published items, Scribus is a little tricky but it works well. You can record your voice or musical instruments into Audacity and make wave or OGG files. You can import Photoshop files into GIMP, Illustrator files into Inkscape (after you download some filters), and any file made in Microsoft Office. Linux is quite versatile.