Highlight Text With Textbox Control

I'm using VB6 against an SQL Server database.
I have a small routine which, if a user enters an invalid value, checks for a valid numeric number,resets the textbox to zero, and sets the focus to this field.
I'd like to highlight this section of text for the user, too.
Is there a way to do this with a normal textbox control or do I have to use a richtextbox control?
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Here's my routine in the LostFocus() event:
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If Not IsNumeric(txtAdjFundingAmt) Then
        MsgBox "Please Enter A Numeric Value", , "Adjusted Funding Amount"
        txtAdjFundingAmt.SetFocus
        txtAdjFundingAmt.Text = 0
    Else
        txtAdjFundingAmt = Format$(txtAdjFundingAmt, "###,###,###,##0")
    End If
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I tried the richtextbox but it didn't like my error-checking routine and didn't allow the user to exit the textfield after an incorrect entry.

Thanks in advance.
John