----------------------------------------------------------------------

First, what is going wrong is the structure for an Arg is (essentially)
	typdef struct
	{	
	    String	name;
	    long	value;
	} Arg;

and the code:
	Arg	arg;

	XtSetArg (arg, "name", 3.2)

expands to
	Arg	arg;

	arg.name = "name";
	arg.value = 3.2;

you can see that with normal C type conversions, the arg.value
gets the integer "3" instead of the floating point value "3.2".  When
the value is copied into the widget resource, the bit pattern is
wildly different than that required for a floating point value.  So,
how to get around this?

The following macro is from the Athena widgets document and I am now
recomending it over the previous suggestions.

#define XtSetFloatArg(arg, n, d) \
    if (sizeof(float) > sizeof(XtArgVal)) { \
        XtSetArg(arg, n, &(d)); \
    } else { \
        XtArgVal *ld = (XtArgVal *)&(d); \
        XtSetArg(arg, n, *ld); \
    }