I may have found an alternative but need some more info on it from you pros out there

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So my other half has a old dell laptop running vista, am I able to clone the hard drive/OS and run it on my MacBook using VM Fusion?
- if I can, will I be able to run the clone on my Mac and her still be able to use that old laptop?
- running a clone can I buy the windows 7 upgrade and upgrade the vista to 7 on my Mac?
- if that dell laptop has problems (running slow, or anything else like viruses or anything) will that port onto my Mac as well? Or will it run a little better being my Mac has better hardware, more hdd space & ram etc?
I like the convenience of it being on one laptop rather then having 2 different laptops. If I can do this I would like to save the money. But if its far better to just do what I had planned before (buy windows 7 retail) then I will stick to that. Thanks in advanced. if its not even possible then thanks for the help.