If the Windows Explorer process crashes as regular as it does, it indicates a serious problem - either a faulty installation or possible even hardware problem.
So I would indeed take it back to the shop as Kipi states, and demand them to fix it
Also - I would imagine some companies (even reputable) just put Vista on their new computers without actually knowing if they are Vista ready, and if the hardware is supported. So it would be interesting to know which computer (specifications) you actually bought.