I have a Dell computer with Vista installed. Nothing but problems. If I install windows XP or windows 7 do I have to delete Vista first? If so, do I lose everything? Or can I install new program first ? Thanks, JJF

Back up your data you need, then delete the partition and do a full format when installing a new OS (that will give you the least longterm problems). If you go to 7, make sure there are drivers available for it. Not all Dell machines have windows 7 drivers or will.

Hi, there are options to install another Operating System parallel to an existing one, but they are very complicated for sb. Who is not an expert.

Windows 7 can be bought as an Upgrade-Version. It can upgrade the existing Vista to Windows 7 and keeps all the programmes and settings.
Make sure that you buy the right Upgrade package for your Vista-Version.
If you have Vista Home get Windows7 - Home Upgrade or Ultimate Upgrade
If you have Vista Business get Windows7 - Professional Upgrade or Ultimate Upgrade
If you have Vista Ultimate bet Windows Ultimate Upgrade
But honestly an upgrade isntallation might not fix all the vista-bugs. The best way to get a stable system is to make a clean installation from scratch.
Safe your important data to a flashdisk first.
Also check on the dell page if there are drivers for windows7 and download them on a flashdisk before you install windows 7.
A downgrade installation to XP is not possible!
If you want to make sure that you can always go back to the old installation you can make an image first. There are several simple tools available like Acronis e.g.