Thanks Has. Just saving the link.
http://scphillips.com/cgi-bin/day.cgi (http://scphillips.com/cgi-bin/day.cgi)
Basically this handy thing will tell you what day of the week a specific date you input was on.
http://www.timeanddate.com/date/dateadd.html (http://www.timeanddate.com/date/dateadd.html)
This one on the other hand lets you add/subtract dates.