your question (the last one) is very broad and would require you to probably hire someone to do it for you. It is not so easy to host on windows 2003 for multiple users with php and asp.net as well as mysql since it requires some experience as well as knowledge of how things work.
You can download and isntall both php and mysql for free. You can also include the mySqlDriverCS for asp.net which will allow users to connect to mysql dbs without ODBC.
You can put it on your pc. If you have windows 2000 or windows xp professional, you can install the webserver component called Internet Information Services (IIS). You can do this from the control panel in add remove programs>add remove windows components. If you dont have win2k or XP pro, you can download a webserver called apache.
Either way, search on google for something like "setting up apache in windows". After you setup the webserver, look at the installation guides for mysql and php. They have instructions for apache and IIS