If you are wanting to only collect it for your own reference, putting:
Date()
will give you the standard javascript date string, something like:
"Mon Dec 28 2009 11:16:03 GMT-0600 (Central Standard Time)"

For anything beyond that, you would need a custom function in the custom code block, that you then call in the formula section of your form, such as (this formats to Salesforce's expected format):

<script>
function sf_date(){
var now = new Date();

var dy = now.getDate();
var mo= now.getMonth()+1;
var yr = now.getFullYear();

var ind = "AM";
var hr = now.getHours();
if(hr >= 12){
ind = "PM";
hr = hr - 12;
}
if(hr == 0){
hr = 12;
}
var min = now.getMinutes();
if(min < 10){
min = String.concat("0",min);
}

return mo+"/"+dy+"/"+yr+" "+hr+":"+min+" "+ind;
}
</script>

Then add the following formula to the fields you wish to have Salesforce formatted current dates:
sf_date()

Let me know if you need further assistance,
FA Support.