I have Ubuntu 10.04 LTS on my laptop installed with the option to boot windows vista when I want to. How can I install Ubuntu 12.04 LTS exaclty where I have Ubuntu 10.04 LTS now without changing/affecting anything else?
Install 12.04 on the partition that you have 10.04 on. However, you will lose all your installed softwares in 10.04. If you don't want that, you will have to go for a distro upgrade. But that might result in a lot of problems which you can find on this site itself. If you want the the softwares on 10.04 installed on 12.04 too, refer to this : How can I duplicate my existing software packages on a new system?
Why not just upgrade to 12.04 if the goal is to swap 10.04 with 12.04. My buddy used a live disk to replace 11.10 with beta 2 and it acted like an upgrade instead. To initiate upgrade via manager hit alt+f2 then type