Regular expressions (Regex) in Dot.Net 1.1

Hey, I need to create a regular expression with this rule: SpecificString_1_AnotherSpecificString. (the asterisk is any string in any length). how do I enforce such a rule using Regex.IsMatch()? (derives from System.Text.RegularExpressions) I thought it should go like this: “SpecificString._1_..AnotherSpecificString” but it seems it passes things that shouldn’t be passed.. Thanks!