Any dud laptops .....

Out there?

Hello folks.
Several questions.

I've been offered a second hand 3 year old but hardly/rarely used laptop with wifi.

I do not know the brand or model yet but will shortly. It will probably be running Vista.

But it will likely be a HP, Compaq, Acer, Asus or Toshiba.

1)Have there been any dud models of these brands that i should stay away from?

If it is running Vista i will probably replace the OS with Win7.

2)If i do replace the OS with Win7 are there any precautions regarding wifi or other machine related drivers i should take?

Any info greatly appreciated.
Greets.
Fotonut.
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