1. It could technically, but can't in reality due to the same origin policy. This applies to both reading and writing external content. The best you can do is load an iframe with a different domain's page in it - but you can't access it programmatically. You can work around this in IE, see Andy E's answer.

2. Yes for the first part, mmmm not really for the second part - you can submit a form to a HTML page and read GET arguments using Javascript, but it's very limited (recommended maximum size of data around 1024 bytes). You should probably have all the intelligence on one page.

3. You can generate a file locally for the user to download using Downloadify. Generating a file and uploading it to a server won't be possible without user interaction. Generating data and sending it to a server as POST data should be possible, though.

4. This is very, very difficult. Due to security restrictions, in most browsers, it's mostly not possible without installing an extension or similar. Your best bet might be Internet Explorer's proprietary scripting languages (WScript, VBScript) in conjuction with the "security zones" model but I doubt whether the execution of local files is possible even there nowadays.

Using Internet Explorer with a local file, you can do some of what you're trying to do:

1. It's true that pages are limited by the same origin policy (see Pekka's link). But this can be worked around in IE using the WinHttpRequest COM interface.

2. As Pekka mentioned, the best you can manage is GET requests (using window.location.search). POST request variables are completely unobtainable.

3. You can use the COM interface for FileSystemObject to read & write local text files.

4. You can use the WScript.Shell interface's Exec method to execute a local program.

So just about everything you asked is attainable, if you're willing to use Internet Explorer. The COM interfaces will require explicit permission to run (a la the yellow alert bar that appears). You could also look at creating a Windows Desktop Gadget (Vista or Win 7) or a HTML Application (HTA) to achieve your goal.

Failing all that, turn your computer into a real server using XAMPP and write your pages in PHP.

see i got what you want to dobest things is do following

1. choose a javascript library (eg:jquery,dojo,yui etc), i use jquery.this will decrease some of your load
2. inspite of saving forms data in in a local file, store them in local variables process them and send them to server (for further processing like adding/updating database etc) using XMLHttp request, and when webservice returns data process that data and update dom.

i am showing you a sample

--this is dom

Name:<input type='text' id='name' /><a href='javascript:void(0)' onClick='submit()'>Submit Form</a><br><div id='target'></div>--this is jsfunction submit(){var _name=$('#name').val();// collect text box's data//now validate it or do any thing you wantcallWebservice(_name,_suc,_err);//above call service fn has to be created by you where you send this data//this function automatically do xmlHttprequest etc for you//you have to create it ur self }//call this fn when data is sucessfully returned from serverfunction _suc(data){//webservice has returned data sucessefully //data= data from server, may be in this case= "Hello user Name"; (name = filled in input box);//update this data in target div(manipulate dom with new data);$('#target').html(data);}function _err(){//call this fn when error occurs on server}

// in reality most of the work is done using json. i have shown u the basic idea of how to use js to manipulate dom and call servcies and do rest things. this way we avoid page-reloads and new data is visible to viewer