Send to all in inbox?

Create a distribution list and add whoever you choose.
When composing new mail just add the distribution list into the TO: field.

Ooops..

Do you mean replying to everyone at once?

I think you want to send an email to all people who have emailed you ..

It would be easy to send an email to everyone if all those people who have sent you are in your contact list .Once they are there in the contact list,then go to view ---> current view --> by category

now go there and you should see all your contact email address in some category depending on what you have named

then select all the categories and drag it to inbox. I mean just drag and drop it on the name "Inbox"
Now it will compose  a new email ,you can send that email

I have 200 emails in my inbox. I cannot go into each email, copy the email, then add it to my contact list one by one. Is there a software that does it? or a an add-on? or module in outlook that will do this?

check out tools section here http://www.slipstick.com/contacts/addauto.htm
mainly "add email address"

You can accomplish this through a several step process that involves a message template, categories, and a client side rule.  Basically, you would select all of the e-mail you want to reply to, right-click and assign to a category, and then run a rule that looks for that category and replies with an .oft Message Template.  I can provide the step by step instructions for Outlook 2003, but I want to make sure that's the version you have.