It's not really difficult to run classic ASP on Internet Information Server 7, but there are some bumps down the road. Here's a little help to get you started:
First of all, check whether you have the Windows feature for ASP installed. Go to Programs and Features in Control Panel and click Turn Windows features on and off. Navigate down the tree of features and make sure ASP is checked.
Next, go to Internet Information Server (IIS) Manager (run inetmgr from the Start Search box to get there fast) and create a new application pool for ASP.
This should be a "No managed code" and "Classic" app pool if you do not intend to mix and match the .NET Framework and ASP.NET in the same pool. The Integrated pipeline would not make sense, because it only applies to integrating HTTP modules that are either native or managed .NET implementations.
I had some difficulties setting the identity of the application pool to the new built-in IUSR account. This account replaces the former computer account called IUSR_machinename. Same goes for the IIS_WPG group for application pools that is replaced by the builtin group IIS_IUSRS. Read more about it here. Under the Advanced Settings of the "ASP" application pool you will find the Identity property under Process Model. The default value is NetworkService. I found no way to set this to the BUILTIN\IUSR by choosing SpecificUser and setting BUILTIN\USR under Identity SpecificUser Credentials. I guess that you shouldn't be running ASP sites under IUSR anymore. It is used for anonymous users automatically.
To easy the administration effort, there is a way to turn off the IUSR account without turning off anonymous identification:
appcmd set config -section:anonymousAuthentication -userName:"" --password
And lastly, create your new web application. For example, copy the ASP site folder under C:\inetpub\wwwroot, where the default installation location of "Default Web Site" of IIS. Convert the folder (or virtual directory) to an application and choose "ASP" as the application pool. Check whether the .asp extension is mapped to the correct handler and whether it is enabled. Also make sure that the identity of your application pool has sufficient rights (and no more than that) to access the files in the web site's folder.
One final note: whenever there is a error in the ASP website, and you get this error message: "An error occurred on the server when processing the URL. Please contact the system administrator",
it's probably because by default no error messages are sent to the client in IIS7. Change the setting "Send Errors To Browser" of your web application under the ASP icon to reveal such errors.
Side note: if you get the nice Internet Explorer 500 error message and no particular details at all, remember to uncheck the "Show friendly HTTP error messages" checkbox under Internet Options, Advanced of IE.