Thanks XpXpert for this - seems your not only an expert in xp....
XpXpert pointed something out to me : if we look at previous releases of windows -say xp and 2k we can see a 1 digit increase - i.e. the code names have gone from 5.0.0000 (2k originally, its now 5.0.2195) to 5.1.0000 (windows XP). So, if we look forward to the next windows release, "longhorn", we see something interesting; Build 3621 is actually 5.2.3621, so we see an advancement in the figures; this would indicate a major update / change to the Kernel, and GUI - although thats not to say we didnt supsect this already. This change will be reflected in .Net. This latest build represents only bug fixes from the previous build, yet i hear on IRC that various cracks that were being used no longer work on it - this is un-confirmed. The next kernel will be "blackcomb" - which would be 6.0.0000 - many new things are expected of this, especially a new file system.
It would appear that microsoft is looking to the future; who knows what it will bring....