Assuming you're looking for free solutions, here are some suggestions used in past (very old) project of mine:
ASP Profiler component. This is a line-level performance profiler for Active Server Pages (with VBScript) code. It shows how your ASP page runs, which lines are executed how many times, and how many milliseconds each take. Especially for heavy data-driven pages, you can see exactly which lines slow down the page, and optimize where necessary.
Googling around I have also found a couple of very old articles on timing/profiling ASP execution code: have a look here and here.
If you have an issue with server side code being slow I have found it is almost always the database causing the issue. You need to check for SQL which is slow to return a result; if you find any you need to look at applying new indexes to your tables. If your app is too chatty with the database you need to look at reducing the number of calls to the database. To find these problems you can always use SQL Server Profiler; this comes bundled with SQL Server 2005/2008 Developer edition.
Also you can use a free SQL Profiler available at xsqlsoftware.com
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