Selected Answer
Once you get the value from the combo box, you can loop through the columns that have the data for which youa re searching like this:
Sub test()
'get the range through which we want to loop
Set cell_range = Range("A1:A10")
'start the loop
For Each cell In cell_range
'you are now inside the loop
If cell.Value = comboboxValue Then
Cells(cell.Row, cell.Column + 1).Value = textboxValue
End If
'continue the loop
Next cell
End Sub
A1:A10 is the range to go through to find the value.
comboboxValue should contain the value from the combobox.
textboxValue should contains the text box value.
cell.Column + 1 is how many columns to the right of the column that you just searched through to put the value. +1 means 1 column to the right; +2 means 2 columns t othe right, etc.
This is the framework of the macro that you will need and it should get you almost all the way there; just make sure this runs when the command button is clicked.