Dual-boot (or triple-boot, or quad-boot, etc..) is when you get a menu at power-on, and you select one OS, be it Windows or a Linux or whatever, and boot that one OS.
NON-dual-boot can take several formats. You might have installed Ubuntu INSIDE XP, using Wubi for example, or maybe inside a "virtual machine" - or maybe you installed XP inside a virtual machine which is running on Ubuntu?
So, please clarify for us, which way you have your OS's installed, and precisely what the current problem is (if there is one -- something about sound card drivers? For which OS?). Perhaps then some members will be able to advise on what you should do next, or what to look out for when you go to re-install one or both OS's.