In light of other recent Windows upgrades (i.e. SBS2008) that are 64 bit only, the new version of SharePoint, when it becomes, available will also only be 64 bit. This will basically mean it will only run on Windows Server 2008 or better.
The reason I mention this is because if you are planning to build a SharePoint solution now it is probably a very good idea to consider a 64 bit environment. Windows SharePoint Services is already available in a 64 bit version so you could install it today and be prepared for when the new version become available.
It is my understanding that Service Pack 2 for the existing version of SharePoint v3.0 will be available in the first half of the 2009. However, you may want to consider making the move to a 64 bit platform today rather than when the new version of SharePoint is released.