I had a look in the System properties of one of the workstations in a computer room at my college today, as it was one I hadn't used since they got some new machines and I was interested to see the specs, and I noticed that their PID is of the form XXXXX-641. Now I thought that only XXXXX-640 was a PID generated from a valid VLK, and that XXXXX-641 to XXXXX-649 were PIDs from keys that can be used to install XP but have never been issued (so must have come from keygens or somewhere?), and so are blacklisted.

I tried to validate it using the WGA site but it said that validation could not be performed (not sure why, as it's XP and IE (7), which is what it was saying I had to be using in order to validate). I also had a look in the system32 folder and found that the "WGA Notifications" update is installed, and there are no WGA-failure "notifications" showing on any of the machines. And they’ve got IE7 installed, so they must have passed WGA at some point recently.

So have MS started issuing keys that generate PIDs of XXXXX-641 now?

From what I've seen, many Educational and Action Pack licenses are using PIDs xxxxx-641 to xxxxx-643. I'm pretty sure what you're seeing is normal.

I've personally only had usage of 4 genuine VLK keys used for various
schools/uni's in my general area, all of them produced the 640 PID when
re-using them on other systems, yet I have read on other forums of MS
supposedly issuing keys that produced other PIDS & people having
problems with them, only to be re-issued new keys when either
Sp1 or 1a came out...
There is a page on MS that lists some of the the Naughty PIDs

I've used 2 genuine VLK keys, and have had one produce a 640, and the other , a 643 pid. The 640 pid was on a VLK educational license of XP Pro. The 643 pid was on a charity-VLK license for XP Pro.

Microsoft offers an ActionPack, to OEMs and business partners... some of the keys that I've gotten from that pack have registered with 643 pids. I cannot remember which ones, unfortunately.

Strange that there are a few out there that produce ones other than 640 - when I saw it I assumed MS must have recently started on a new batch of keys or something (having sold so many copies of XP?!), as I've seen things before saying that they've never issued any that don't produce 640.

I've always thought that Partner Action Pack that you refer to lactually looks to be reasonable value for money as you get legit copies of everything with it and it only costs a few hundred pounds (although apparently you only get Vista Business, not Ultimate).