the more recent versions, actually probably LTS 6 (about to have 9), have a partition manager start when you run the install program - it will allow you to partition up the disk and yep keep the windows partition - I've had a few issues before with the boot loader not choosing to include windows, but that doesn't happen often - the people who created Ubuntu understand most people dual boot - even I do, though I hardly ever boot windows (well I guess I do for games occasionally, but not often)