I've used ASP (or what is now called "Classic ASP") for a while. I like it, but I've been reading and experimenting with ASP.Net. It is not only very cool, but has some real advantages over classic ASP.
Firstly, it's part of Microsoft's long term strategy for internet applications. This means that all the new goodies will be focused on ASP.Net, not on Classic ASP.
Secondly, it is more efficient than Classic ASP (particularly with large pages) because you can use it to change the data on your page without reloading the page. This saves server time constructing the page, browser time formatting the page and traffic on the Internet. Essentially the client can take action that just requests new data be displayed in a given part of the page while leaving the rest of the page unchanged.
But, before you do anything, make sure your ISP can support it. That includes not only your choice of language (ASP, ASP.Net, PHP, etc.) but also the database (mysql, MS SQL, etc).