Yes, I'm answering my own question, but I haven't found it here yet and thought this was a rather slick thing:
...in VB.NET:
String.Join(",", CType(TargetArrayList.ToArray(Type.GetType("System.String")), String()))
...in C#
string.Join(",", (string[])TargetArrayList.ToArray(Type.GetType("System.String")))
The only "gotcha" to these is that the ArrayList must have the items stored as Strings if you're using Option Strict to make sure the conversion takes place properly.
EDIT: If you're using .net 2.0 or above, simply create a List(Of String) type object and you can get what you need with. Many thanks to Joel for bringing this up!
String.Join(",", TargetList.ToArray())
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