You can do a virgin install from the upgrade disks. Search ZDNet.com for Ed Bot’s article for one example. It works. It basically involves doing a double install, but not activating after the first one. With Win 7, it doesn’t take very long for the two.
Windows uses weighted criteria to determine whether a change or bunch of changes is another system, or just a minor upgrade or maintenance. I have sometimes changed several components without any issues.
In any case, they will not hassle you if you ring for an authorisation. Let’s face it, if you were using a pirate copy, you would not be likely to ring them. The only time they actually queried me was when I was getting a second copy of Office activated when they already had it recorded as activated, but since it was within the full licence conditions of allowing a copy on the laptop of the primary desktop user, they had no objection there either.
Note that the full licence allows you to legally transfer it to a new machine, whereas the OEM version is only for the machine on which it was originally installed. If you built your own machines, they effectievly become like Anderson’s axe - had two heads and three handles replaced! It is still the same machine, your honour!
As for Anti-virus, I run dual boot Win 7, without hidden partitions, so that running AV (like MSE) or backup from the general boot partition will handle the DAW partitions as well. I only run the firewall and defender from the DAW partition directly, and use IE to access known websites only, like for drivers from MS or RME and updates for software.
Win 7 does not need the DAW optimisations that XP did. Win7 does a lot of optimisations itself, and is much less likely to disrupt realtime streaming. If you had only SSDs, while Win 7 would still have the defrag and ReadyBoost services, they would never be invoked.
We have Win 7 Ultimate and SSDs on all systems. I have disabled Superfetch, Defrag and HomeGroup services on all, and virtual memory on the DAWs as they have plenty of memory. The DAW partitions don’t run Aero either.
I have 64kB sectors on all systems as even with HDDs, they gave 30+% improvements in real transfer times.