Not sure what exactly your stuck on...
If it is the php part; post_['name'] doesn't look correct. Try $_POST["name"]
If that isn't the problem then:
1. Can you output textbox1.text somewhere to see it is getting the correct text?, you'll need to url encode it so that it doesn't cause problem with spaces and special characters!
2. Can you post the php you have so far if the problem is there?