DensifyLine

{A} the Humpty Dumpty method

• Start an Edit session, select the lines,
• choose the Divide command from the Edit submenu. This splits it into a gazillion seperate features.
  
• Project, then
• use Dissovle from Data Management Toolbox.

{B} the Leet C0d3r method, for ArcMap

• Open attribute table for the feature class
• Run Field calculator on [shape] field, using code from this thread (you will need to do some mathmagic to change from percentages to map units in the code)

{C} the Leet C0d3r method, for ArcView3

As above, but much simpler (from the ArcGIS ">same thread):

• edit the [Shape] field, and
  
• calculate [Shape].AsPolyline.ReturnDensified(30) where where '30' is a desired density of 30 map units.

There is a feature request at least far back as 2002 to optionally allow Project Management to densify before projecting, see geographic 2 projected (curvey line).

{D} ogr2ogr -segmentize

I asked the gdal-dev mailing list if ogr had a similar function, and within hours ogr2ogr -segmentize came into being, with r14881 -- thank you Even Roualt! There is also densify.py by Howard Butler which only works on LINESTRINGs at the moment and isn't as cool as Even's solution. It does have a few fancier options about what to do with the slop if you want exactly regular intervals though.