Change Sharepoint main page name without changing URL

If you create a custom list definition, you can define your own create/edit/list pages. Take a look at the schema.xml in an existing list definition feature, such as DocumentLibrary. For each View there's a SetupPage attribute which points to the list page, and there's a Forms section at the end where you define the DisplayForm, EditForm and NewForm. 'pages\form.aspx' and 'pages\viewpage.aspx' refer to the 12\template\pages folder.

Sharepoint sites should be able to run on any port- if you go into Sharepoint Central Admin and create or delete web applications without a problem.

Is it your intention to run heterogenously with Sharepoint and your regular site both on Port 80? I know that you can create a web application on 80 and then not have a root site collection ( Sharepoint applications consist of a Web Application that runs on a certain port and any number of Site Collections within that, each of which has it's own directory path and can contain lists, libraries, other Site Collections and so on ) just creating one on a different path, but I don't know for sure how that would work alongside an existing web site on the same port- it may not play nice. Again, you can create and delete site collections from the Sharepoint Central Admin page, which is linked from your Administrative Tools list on your server.I would try this first, as if it works it's an easy solution.

Is Windows Search Server Express related to Sharepoint's own search facilities? If it is you may find that it expects to run using some of the Shared Service Provider facilities, which even Sharepoint doesn't expect to be running on the same port as the sites it's providing services for.