Liinework will EXTEND (using the AutoCAD EXTEND command) to the wall's justification line (which could also be at the wall centerline, if not at the wall baseline, left side or right side).
You can use the Extend option of the AEC Modify Tools to accomplish what you want. Select your linework, right click, choose AEC Modify Tools > Extend from the context menu, position your cursor over the component edge to use at the extend position and left click and, finally, left click near the endpoint to be extended of one item of linework.
Credit for this answer goes to Steve Bennett, over in the AUGI Forums: http://forums.augi.com/showthread.php?t=73990
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David Koch
Autodesk Discussion Group Facilitator
Using ADT 2004 at work; access to 2005, 2006, 2007 & 2008 at home