Well if you have two separate installations of a operating system on the same hard drive, upon startup there should be a menu asking you to select which operating system you want to use for that session. As you didn't know, partitioning a hard-drive is basically splitting it up into portions, mainly used for installing more than one operating system or leaving a partition dedicated to backup and recovery in case something goes wrong with the main one. Usually, most computers have no partitions, you can find this by easily going into 'My Computer' and seeing how many icons there are under hard drives. Most computers will have just one ( usually "(C:) Local Disk") but in newer computers, some may have factory installed partitions. If you really want to know for sure, search "disk management" in the start menu, then it should come up with something called "Create and format hard disk partitions," click on that and it will show all partitions and information for your hard drive. (Those instructions were for windows 7, I imagine they would be the same for vista, but not entirely sure). Please post back what you find. Hope this helps!