According to ArenaNet, less than 0.05% of the Guild Wars population is stuck on Windows ME or older; but if you're one of these few, it's probably time to upgrade. ArenaNet has announced plans to discontinue Guild Wars support for older Windows versions, meaning Windows ME and anything below that.
In a post on the support forums, Anet's French community manager Stephane Lo Presti posted about the upcoming change, set for June 14. The studio doesn't expect this will affect too many players, given that their logs show the majority are running XP or newer.
Since the launch of Guild Wars in 2005 we’ve stayed locked into our original minimum system requirements. Unfortunately, the game has reached a point where this is preventing us from deploying important features. After serious consideration, we’ve decided that Guild Wars will no longer be supported on Windows 95, Windows 98, Windows 98 SE, and Windows ME beginning June 14, 2012. In order to continue to play Guild Wars after this date, we recommend upgrading to a more recent version of Windows.
Realistically, we do not expect this to impact the vast majority of Guild Wars players. Our logs indicate that fewer than 0.05% of our active players use one of these versions of Windows. Discontinuing support for older versions of Windows allows us to deploy features that will improve account management and security.
System requirements on the Guild Wars site will be updated accordingly, but Presti notes they wanted to give players an advance notice anyway. Well, at least everyone will be ready for Guild Wars 2 when that's out.