Changing the NIC is counts for a lot towards reactivation.
From:
http://www.microsoft.com/piracy/activation_faq.mspx
How does product activation determine tolerance? In other words, how many
components of the PC must change before I am required to reactivate?
Common changes to hardware such as upgrading a video card, adding a second
hard disk drive, adding RAM or upgrading a CD-ROM device will not require
the system to be reactivated. Specifically, product activation determines
tolerance through a voting mechanism. There are 10 hardware
characteristics used in creating the hardware hash. Each characteristic is
worth one vote, except the network card which is worth three votes. When
thinking of tolerance, it's easiest to think about what has not changed
instead of what has changed. When the current hardware hash is compared to
the original hardware hash, there must be 7 or more matching points for
the two hardware hashes to be considered in tolerance. If the network card
is the same, then only 4 additional characteristics must match (because
the network card is worth 3, for a total of 7). If the network card is not
the same, then a total of 7 characteristics other than the network card
must be the same. If the device is a laptop (specifically a dockable
device), additional tolerance is allotted and there need be only 4 or more
matching points. Therefore, if the device is dockable and the network card
is the same, only one other characteristic must be the same for a total
vote of 4. If the device is dockable and the network card is not the same,
then a total of 4 characteristics other than the network card must be the
same.
Are the changes cumulative? In other words, if I change one component
today and one tomorrow, is that two component changes?
The changes are cumulative; however, if a user is asked to reactivate, the
hardware profile is reset to that new configuration.
What are the 10 hardware characteristics used to determine the hardware
hash?
The 10 hardware characteristics used to determine the hardware hash are:
Display Adapter
SCSI Adapter
IDE Adapter
Network Adapter MAC Address
RAM Amount Range (i.e. 0-64mb, 64-128mb, etc),
Processor Type
Processor Serial Number
Hard Drive Device
Hard Drive Volume Serial Number
CD-ROM/CD-RW/DVD-ROM
It looks like you were close, but you still should not have had to
reactivated yet, if Activation was working the way it is supposed to.