Thank you for writing.
RadSpinEditor internally uses MS TextBox for its textbox part, so in order to set a ToolTip to this textbox, you should use the standard ToolTip. Just drop the ToolTip component on your form and then in the form constructor define the tooltip text as shown below:
"Custom ToolTip Text"
Do not hesitate to contact us if you have other questions.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!