Use Javascript.
Say the id of the outside textbox is txtoutside.
Now
OnBlur
or
OnChange
event write
onchange ="javascript:return checkValue(this);"
function checkValue(obj)
{
if(obj){
var elemoutside = document.getElementById('txtoutside');
var thistextval = parseInt(obj.value);
var outsideval = parseInt(elemoutside);
if(outsideval <= thistextval) {
return true;
}
}
alert('Invalid entry');
return false;
}
this would help I think.