there are many ways to do that.one of them is as
follows -

You need to check if the value of the checkbox is
set or not by isset function of php.

ASP.NET controls automatically keep their data
when page is sent to the server in response to
events (like a user clicking a button).
this persistence of data is called view state

if you want to resize your asp.net textbox height according
to content then these codes will help you perfectly.

there are different kind of joins available by sql like
inner join,left join,etc.by the following example i will show
how to do left join which i used in my application to
get data from two tables -

silverlight application are great.you can add silverlight
application in your asp.net project easily.follow the
steps and you will know how to create and add silverlight
applicaiton in asp.net application/website -

in asp.net application there may be different
server errors like file not found,server error,
etc.when those errors happens default ASP.NET error
page is shown which looks odd and users don't
understand what type of errors occured.to overcome
these problems it's a good idea to use own
error files.

connecting Asp.net local MDF database files to sql
server management studio express is easy to do.
following are the steps to do so -