what version of the dll are you using?  i believe we implemented anti-collision labels for PieChart3D in the 7.3 release, and in a hotfix for prior versions.

Indeed, there was an anti-collosion algorithm implemented for 7.3, but it looks like it doesn't quite work for large enough labels and small enough slices. You can submit this as a bug to our developer support group (http://es.infragistics.com/gethelp) and we'll try to find further optimizations to the algorithm, though there will likely be edge cases (there's nothing stopping the users from making the label extremely long) for which it won't work. In the meantime, you can either rotate the chart somewhat or manually insert a line break into the label with a custom label renderer. Documentation of the latter can be found here:
http://help.infragistics.com/Help/NetAdvantage/NET/2007.3/CLR2.0/html/Chart_Customize_Labels_Using_the_IRenderLabel_Interface.html