Simple answer is you can't,without the cd that is specific to your laptops sys config(which MS check's for during install to prevent piracy) your pretty much boned.Someone else's install disc won't work.
With great difficulty I imagine. Don't you have a restore CD with the system? If not that to be legal your into buying a new SO - i would go Win 7 anyway it's better than vista.
No most laptops ( and i suppose desktops now, haven't bought one in a while) come preloaded with the OS and has a certification of authority sticker on the bottom of the laptop. I'm a little limited on cash so no 7 at the moment unless my good aunt who works with the Gates gets it for me.
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You should have some back-up to this - where did you get it, when and why do you want to fully-reinstall?
L