Start with an aspx page that contains just a literal control like this...

<%@ Page Language="vb" AutoEventWireup="false" Codebehind="vCalendarFile.aspx.vb" Inherits="Scheduler.vCalendarFile" %>
<asp:Literal Runat="server" ID="litText"></asp:Literal>


...then in the code behind, during page load...

        Dim dateStart As DateTime = someDateTimeObject
        Dim dateEnd As DateTime = someOtherDateTimeObject
        
        ' Note...Outlook will want GMT times. That's why we need to convert to universal time.
        dtstart = dateStart.ToUniversalTime.ToString("yyyyMMdd\THHmmss\Z")
        dtend = dateEnd.ToUniversalTime.ToString("yyyyMMdd\THHmmss\Z")
        location = Helper.GetLocationName(_locationID)
        description = "This appointment was generated=" & vbCrLf & _
                      "to serve as a reminder of your registration time. Click the 'Save and =" & vbCrLf & _
                      "Close' button above to enter this appointment into your calendar."
        summary = " PUT SUBJECT OF THE REMINDER HERE"
        fileName = "PUT NAME OF THE GENERATED VCS FILE HERE"
        
        Dim content As New System.Text.StringBuilder

        content.Append("BEGIN:VCALENDAR")
        content.Append(vbCrLf)
        content.Append("PRODID:-//Microsoft Corporation//Outlook MIMEDIR//EN")
        content.Append(vbCrLf)
        content.Append("VERSION:1.0")
        content.Append(vbCrLf)
        content.Append("BEGIN:VEVENT")
        content.Append(vbCrLf)
        content.Append("DTSTART:")
        content.Append(dtstart)
        content.Append(vbCrLf)
        content.Append("DTEND:")
        content.Append(dtend)
        content.Append(vbCrLf)
        content.Append("LOCATION:")
        content.Append(location)
        content.Append(vbCrLf)
        content.Append("DESCRIPTION;ENCODING=QUOTED-PRINTABLE:")
        content.Append(description)
        content.Append(vbCrLf)
        content.Append("SUMMARY:")
        content.Append(summary)
        content.Append(vbCrLf)
        content.Append("PRIORITY:3")
        content.Append(vbCrLf)
        content.Append("END:VEVENT")
        content.Append(vbCrLf)
        content.Append("END:VCALENDAR")

        Me.litText.Text = content.ToString()

        Response.AddHeader("content-disposition", "inline; filename=" + fileName + ".vcs")
        Response.ContentType = "text/plain"