The highlight function searches through the string passed to it for either a string or array of keywords.
It highlights the keywords found in the string by wrapping them in HTML SPAN tags.
If an array of keywords is passed to it, it highlights the matches in the order of longest keyword to shortest.
Setting the boolPhrase argument either false or true an highlight of any word or exact phrase is performed respectively.

strHighLighted = HighLight(stringToHighlight, strKeywords, boolPhrase)

Arguments:
stringToHighlight = string to highlight
strKeyWords = word or array of words to highlight (separated by space or comma)
boolPhrase =
true = exact phrase
false = any word

Change the variable:
HlColor = "yellow"
with the highlight background color you prefer

<%
Dim a, strText

strText = "Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Praesent vehicula.
Nam rem risus, scelerisque condimentum, ultricies sed, pharetra commodo, nibh.
Suspendisse eu purus sit amet velit facilisis gravida. Nulla magna nulla, convallis vel,
congue id, tempor et, ipsum. Nunc rhoncus."

a = highlight(strText, "gravida adipiscing lorem", false)

Response.Write a
'--- returns 4 highlighted word matches
%>

<%
Private Function HighLight(ByVal strToHighlight, ByVal strKeywords, ByVal bPhrase)
    '--- strToHighlight = string to highlight
    '--- strKeyWords = word or array of words to search for
    '--- bPhrase = highlight: true=exact phrase, false=any word
    Dim i, j, iKwd, strkwd
    Dim matchPos1
    Dim matchPos2
    Dim matchPos3
    Dim badChar
    Dim strBegin
    Dim strEnd
    Dim tempStoreKeyword
    Dim objKWRegExp
    Dim objLRegExp
    Dim objStripHTMLRegExp
    Dim HlColor
    HlColor = "yellow" '--- highlighting bgcolor
    Set objStripHTMLRegExp = New RegExp
        objStripHTMLRegExp.IgnoreCase = True
        objStripHTMLRegExp.Global = True
        objStripHTMLRegExp.Pattern = "<\S+>"
    strToHighlight = objStripHTMLRegExp.Replace(strToHighlight, " ")
    Set objLRegExp = New RegExp
        objLRegExp.Global = True
        objLRegExp.Pattern = "(\+|\?|\$|\(|\)|\.|\||\{|\}|\[|\]|\^|\*|\\)"
    Set objKWRegExp = New RegExp
        objKWRegExp.IgnoreCase = True
        objKWRegExp.Global = True
    strKeywords = Trim(strKeywords)
    strKeywords = Replace(strKeywords, ",", " ")
    strKeywords = Replace(strKeywords, ";", " ")
    If Not bPhrase Then
        strKeywords = Split(strKeywords, " ")
    End if
    If Not IsArray(strKeywords) Then
        strKwd = Replace(strKeywords, """, """")
        objKWRegExp.Pattern = "()(" & objLRegExp.Replace(strKwd, "\$1") & ")()"
        strToHighlight = objKWRegExp.Replace(strToHighlight, "$1<span style='background-color: " & _
        HlColor & ";'>$2</span>$3")
    Else
        For i = 0 To UBound(strKeywords) - 1
            For j = i + 1 To UBound(strKeywords)
                if Len(strKeywords(i)) < Len(strKeywords(j)) Then
                    tempStoreKeyword = strKeywords(i)
                    strKeywords(i) = strKeywords(j)
                    strKeywords(j) = tempStoreKeyword
                End if
            Next
        Next
        Do While (iKwd <= UBound(strKeywords)) And (InStr(strToHighlight, "<span") = 0)
            objKWRegExp.Pattern = "()(" & objLRegExp.Replace(strKeywords(iKwd), "\$1") & ")()"
            strToHighlight = objKWRegExp.Replace(strToHighlight, "$1<span style='background-color: " & _
            HlColor & ";'>$2</span>$3")
            iKwd = iKwd + 1
        Loop
        For i = iKwd to UBound(strKeywords)
            matchPos1 = InStr("<span style='background-color: " & _
            HlColor & ";'></span>", LCase(strKeywords(i)))
            matchPos2 = matchPos1 + Len(strKeywords(i))
            matchPos1 = matchPos1 - 1
            matchPos3 = InstrRev("<span style='background-color: " & _
            HlColor & ";'></span>", LCase(strKeywords(i))) - 1
            if matchPos1 > -1 then
                if matchPos3 = matchPos1 then
                    badChar = Mid("<span style='background-color: " & HlColor & ";'></span>", matchPos1, 1)
                    if badChar <> " " then strBegin = "([^" & badChar & "])(" Else strBegin = "()("
                    badChar = Mid("<span style='background-color: " & HlColor & ";'></span>", matchPos2, 1)
                    if badChar <> " " then strEnd = ")([^" & badChar & "])" Else strEnd = ")()"
                    objKWRegExp.Pattern = strBegin & objLRegExp.Replace(strKeywords(i), "\$1") & strEnd
                    strToHighlight = objKWRegExp.Replace(strToHighlight, "$1<span style='background-color: " & _
                    HlColor & ";'>$2</span>$3")
                end if
            else
                objKWRegExp.Pattern = "()(" & objLRegExp.Replace(strKeywords(i), "\$1") & ")()"
                strToHighlight = objKWRegExp.Replace(strToHighlight, "$1<span style='background-color: " & _
                HlColor & ";'>$2</span>$3")
            end if
        Next
    End If
    HighLight = strToHighlight
End Function '--- HighLight
%>