CODE
string getDay(string date) // date must be in the form "mm/dd/yyyy"
{
list datesplit = llParseString2List(date,["/"],[]); //mm/dd/yyyy\
integer month = llList2Integer(datesplit,0);
integer day = llList2Integer(datesplit,1);
integer year = llList2Integer(datesplit,2);
integer a = (14-month)/12;
integer y = year - a;
integer m = month + (12 * a) - 2;
integer returnval = (day + y + (y/4) - (y/100) + (y/400) + ((31*m)/12)) %7;
if(returnval == 0) return "sunday";
if(returnval == 1) return "monday";
if(returnval == 2) return "tuesday";
if(returnval == 3) return "wednesday";
if(returnval == 4) return "thursday";
if(returnval == 5) return "friday";
if(returnval == 6) return "saturday";
else return ""; //invalid date
}
Many thanks to David Trimboli for the 'C' (I think) code (found his site through google).
His site.
If anyone finds any mistakes/optimizations they'd like tom make, feel free to do so

-Chris
P.S. This also works with leap years
