But if you read the EULA all versions of OEM Windows are tied to the Original Hardware that they where installed on. So if you change any of that hardware even a Data Lead to a HDD Technically you should buy a new License.
The reality of how M$ Legal addresses this issue though is that provided you are not making any [b]Major Performance Improvements[/b] they will not worry too much as they have to allow for failed hardware to be replaced. According to M$ Legal in AU they will accept Repairs to Computers and still retain the OEM Software but if you Upgrade the system you have to buy new Software.
If your friend is overly concerned they can purchase a Retail Version of 7 which is allowed to be installed on 2 Computers and bypass the Problem with buying the cheaper OEM Product.
Of course if your Friend goes ahead and buys a OEM Copy and then changes the Hardware and is caught by M$ Legal s/he will be facing a major issue with M$ Legal demanding that they pay them a Lot of Money and allow their names to be Published in the M$ Enforcement Alerts in the country where the Piracy Occurred. This also includes your friends Home Address Details. ;)
I'm not sure what the Domestic Penalties are for Piracy but M$ hits companies $250.000.00 for a first offense.
Of course if you are involved in the Piracy by installing the Software to new Hardware you will also be involved in any action instigated by M$ Legal against your Friend and will be subject to the same penalties. So if you are a Professional IT Person who works for yourself you could end up paying considerably more in Penalties than the person who is using the Pirated Software.
Col