User Form Basics - Populating Text Boxes

If anybody has a link to a good tutorial on user forms, it would be greatly appreciated. Failing that...

I am trying to create a user form to edit some named ranges. The VBA user form designer is basically the same as Borland Delphi, so building the form itself was easy. What I can't figure out is how to populate the user form with the data from the spreadsheet.

I have a number of text boxes on the form with names like txtTier1Slots, txtTier1Ceiling, txtTier1Floor, etc up to 4.

I have a defined name that corresponds with each item, Tier1Slots, Tier1Ceiling, Tier1Floor, and so on. I'm using defined names because they're referenced in Conditional Formatting on one of the worksheets in my project. They don't exist as actual cells, just name references.

I want to get the form populated with those values. I've tried about twenty variations of the following code, using ThisWorkbook, Workbooks, Cells, Range, Name, and just about every cell reference method I can think of. I've so many different error messages, my head is spinning.

Private Sub UserForm_Initialize()
    frmRaceLimits.txtTier1Slots.Value = ActiveWorkbook.Cells("intTier1Slots").Value
End Sub

Any thoughts?