Craig,
Like all of the other brain-dead functions in VFP that use memo fields to store stuff you are limited to about 256 characters. There is no limit to the size of a string in a property, but as the others suggest you'll need to assign it in method code instead of using the prop sheet.
Why the heck they don't SET MEMOWIDTH 1024 inside the VFP code I'll never know!
>Is there a limit to the number of characters that can be entered into the RowSource property of a listbox?