The regular expression class that is part of the .NET Framework (System.Text.RegularExpression.Regex) provides many advanced regular expression capabilities not found in the regular expression library used by VBScript and JScript in classic ASP. Some of the advanced features include named captures, non-capturing, lookaround, pattern comments, and Replace() method delegates.
Darren Neimke has authored an excellent article highlighting these advanced features: Regular Expressions in .NET. Darren's article is for those who have had a good deal of experience with the regular expressions. If you are still new to regular expressions, you may want to hold off on this article until you are more familiar with the syntax and semantics of the standard regular expressions.