I need help with regular expressions

I used regular expressions long ago. Since not using it that frequently, I'm not that good with it. May some one help me coding this one? I am using VWD and Visual Basic. My regular expression is not for behind the code but is for a textbox control and I hope to include it this way:
<asp:RegularExpressionValidator ID="CompanyNameRegularExpressionValidatorDoNotAllow" runat="server" ControlToValidate="CompanyNameTextBox" ErrorMessage="Some special ..........." ValidationExpression=" REGULAR EXPRESSION CODE TO BE INCLUDE HERE ">Some special .......... </asp:RegularExpressionValidator><br /> This is what I need:
1) Do not allow blank space, tab or any other kind of space at the beginning of the string. 2) Do not allow more than one space between words and do not allow blank space at the end of the string. ...