This is one of my first Salesforce hacks; this trick will learn you how to load an hidden S-Control on every Salesforce page:

My S-Control is “hidden” using a style sheet command. The “hint” that there is an embedded S-Control is a message on the sidebar that reads “Field Level Help Enabled”.

Basically, you write an S-Control, then create a custom home page component of type “HTML”, choose the “show HTML” checkbox, and type in the following code:

<iframe src="/servlet/servlet.Integration?lid=XXXXXXXXXXX" style="display: none"></iframe>

After you save this change and add it to the home page sidebar, it will execute on any page that includes the sidebar. The “lid” parameter is the ID of the S-Control to execute.

Use this CSS stylesheet for your custom S-Control pages.
Your mod will look like a real Salesforce styled page. (cases tab style)

body {
	font-family:'Arial','Helvetica',sans-serif;
	font-size:75%;
	line-height: 1.6em;
	background: #fff;
	padding: 0;
}

h1,  h2 { font-size: 14px; font-weight: bold; }
h3 { font-size: 100%; background: #DDB929; display: block; padding: 1px; color: #fff; }
h4 { font-size: 80%; background: #DDB929; display: block; padding: 1px; color: #fff; }

label { font-weight: bold; text-align: right;  }
span { }
strong { font-weight: bold; color: #f00; }

a { color: #000; }

hr { color: #eeecd1;  border: 1px solid;}

div {
	background: #F3F3EC;
	margin: 5px;
	padding: 5px;
	border: 2px Solid #eeecd1;
	width: 95%;
}

li{
	 display: block;
	 margin: 2px 2px 2px -20px;
}

table {
	width: 100%;
	background: #F3F3EC;
	font-size: 12px;
	border-top: 5px Solid #E5C130;
	border-bottom: 2px Solid #E5C130;
	border-left: 1px Solid #eeecd1;
	border-right: 1px Solid #eeecd1;
	padding: 0px;
	margin: 0px 0px 10px 0px;
}

th { background: #eeecd1; height: 19px; width: 20%; } // TODO dynamic

td {
	height: 19px;
	border-bottom: 1px solid #eeecd1;
	width: 20%;
	margin: 0px 2px 0px 2px;
	padding: 0px 5px 0px 2px;
}

.classy0 { background-color: #eeecd1; }

button, .btn {
	background-image:url('/img/bgButton.gif');
	background-position:left top;
	background-repeat:repeat-x;
	border-color:-moz-use-text-color #5C5D61 rgb(92, 93, 97) -moz-use-text-color;
	border-style:none solid solid none;
	border-width:medium 1px 1px medium;
	color:#FFFFFF;
	cursor:pointer;
	display:inline;
	font-family:'Verdana','Geneva',sans-serif;
	font-size:80%;
	font-weight:bold;
	padding:1px 3px;
}

.relatedListBlock{
	float: left;
}

.end {
	clear: both;
}

.hide {
  	display: none;
}

These handy Salesforce functions I used a lot, for doing Salesforce database queries.
You can use these functions in your S-Controls:

/**
 * Get an array with all the possible fields names from a object
 * @param objectType object to get the fields from.
 * @return array with all the fieldnames of the given object
 */
function getFields(objectType) {
	var describeSObjectResult, fields, i;

	describeSObjectResult = sforce.connection.describeSObject(objectType);
	fields = [];
	var length = describeSObjectResult.fields.length;
	for (i = 0; i < length; i++)
	fields[i] = describeSObjectResult.fields[i].name;

	return fields;
}

/**
* Result handler, forwards you to the detail page,
* if there is an error give alert message.
* @param result - can be a (sf query) object, or a textmessage string.
* @param idVal - the id of the detailpage to forward to.
*/
function resultHandler(result, idVal){
	var msg = "";

	if (typeof(result) == "object") {
		if (result[0].getBoolean("success")) {
			msg = "";
		} else {
			msg = "Error: " + result[0];
		}
	} else {
		msg = result;
	}
	if (msg != ""){
		alert(msg);
	}
	self.location.href = "/" + idVal;
}

Oh I loved my previous project, where I had to work with the CRM: Salesforce.
Salesforce coding was fun: S-Controls (iframes), Salesforce Ajax (Javascript with Salesforce Query Language) and Apex (Java like Salesforce serverside coding).

These are handy Salesforce date/time functions which you can use in your S-Controls:

/**
* Return the current time
* @return javascript date time object
*/
function getCurrentSalesForceTime(){
	var currentDateTime = sforce.connection.getServerTimestamp();
	currentDateTime = setStringToDateTime(currentDateTime.timestamp);

	return currentDateTime;
}

/**
* Set Javascript Date Time to Salesforce Date Time;
* @param dateTimeObj - date time string
* @return salesforce date time object
**/
function setStringToDateTime(dateTimeObj){
	var dateTimeObj;

	if (dateTimeObj != null) {
		dateTimeObj = sforce.internal.stringToDateTime(dateTimeObj);
	}

	return dateTimeObj;
}

/**
* Set Salesforce Date Time Object to Javascript Date Time
* @param dateTimeObj - Salesforce date time object
* @return string date time
**/
function setDateTimeToString(dateTimeObj){
	var dateTimeObj;

	if (dateTimeObj != null) {
		dateTimeObj = sforce.internal.dateTimeToString(dateTimeObj);
	}

	return dateTimeObj;
}