The following was taken from Inventor 2014 help. Works just like the solidworks symmetry mate, but no width constrant yet.
The Symmetry constraint positions two objects symmetrically according to a plane or planar face.
On the ribbon, click Assemble.
In the Place Constraint dialog box, under Type, click Symmetry constraint.
Select the first geometry to constrain.
Select the second geometry to constrain to the first selection.
Use Select Other to cycle through geometry.
Select the symmetry plane.
If Show Preview is selected, observe the effects of the applied constraint. If either component is adaptive, constraints are not previewed.
Click Apply to continue to place constraints or click OK to create the constraint and close the dialog box.
The following was taken from Inventor 2014 help.
Of course Inventor 1014 didn't exist back in 2008.
You can share your ideas about how to improve Inventor with the Development Team at the IdeaStation link:
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
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How can we put in enhancement requests.
I have found that it is best to provide sample data sets when appropriate.
Thanks for links.