Splitting lines automatically at specific distances using ArcGIS Desktop?

I have a set of polylines which I need to split at varying distances from their starting points.

In general, I'm looking for a something similar to the SPLIT function within the editor tool. There it is possible to specify a certain line length where the split should be applied.

For instance: I have a line A of 3200m length, that I need to split into two separate geometries, one from 0 til 1700m, and one from 1700m til 3200m.

Can this be done in ArcGIS Desktop?

I'm using ArcGIS Desktop 9.3.1. on WinXP with Python 2.7.2.