Manipulating User Input From A Form

I have a HTML page with a form on it. I have an ASP page that processes what a user has entered into the form (updates a database etc).

I now need a page that fits between these two pages to pre-process�the users input. I need to do it this way because I am not allowed to change either of the two existing pages.

I know how to read what the user has input into the form and I know how to pass control onto the next page.

What I have not been able to work out is how to change the user input and have those changes passed onto the next page as if nothing has happened (that is, the original ASP page just performs its request.form(�item�) calls as it always has but instead of seeing what the user actually typed in, it should see the changed text as created by the new pre process� page)

I have tried using a regular expression replace but can only successfully make this change a variable and not the original form input. Equally I cannot find a way of swapping the original form input string with the output variable from the replace.

Does anyone have any ideas on this one?