|"most of the members that are going to be using it prefer VISTA. They don't want to change"|
You said you're upgrading from XP so they are changing. Win7 is very similar to Vista only it's a superior OS & would have been the better choice. Win7 is Vista's smarter, better looking, younger sister. lol
You didn't state whether this system (or systems) meet the minimum requirements for Vista. Having enough memory is very important. The Dell model you quoted only accepts a max of 2GB. If you want your system (or systems) to be productive, you should have at least that amount.
Your Vista ISO MUST be burned to a DVD, it's too large for a CD & cannot be spanned across several of them. ImgBurn will do what you want but you'll need a DVD burner, it's not clear if you have one or not.