That installing Windows is widely discussed. But let me pare it down to the simplest.
1. DO YOUR RESEARCH. Does Dell supply drivers for your Vista 32 bit or 64 bit OS? If not, stop.
2. Installing the Dual Boot is not for the timid I fear and while it's nice you asked, I find that those that ask and didn't research such (the articles are out there) tend to fare poorly or get upset easily.
3. If Dell has the drivers the next step is to look at your Vista DVD. Let's hope it's a RETAIL VERSION because those OEM versions tend to be too much trouble. "WHY?" is noted on the net.
4. Finally you have all the drivers collected and ready to start. The best dual boot installs I've done have me blank the drive with DBAN (a single wipe is good enough) then boot the Windows DVD and install that OS. Then I install the drivers I collected and I'm ready to boot my Linux CD (I do not use the Dell version) and then I follow the notes for that OS (again, these are out there for the reading.) Finally I look at Grub or the bootloader to change which OS is the default.
My sister bought a used Dell PC from a college; there is a Windows Vista sticker on it. When we turned it on, however, it booted from Linux. My sister is no longer young and only wants basic PC and internet functions. (1) How can I determine if the system is dual booted with Linux and Vista. (2) If it is dual booted, how do I make Vista the default OS. (3) I'll buy Windows 7 if necessary, but what would I need to do before installing it.