Hi Kiss Istvan,
The CustomTaskPane's Title property is read-only, so once it's set, it cannot be changed:

Regarding a progress bar that doesn't require too much working space, consider using a Notification Window. This doesn't require any user action (you would make it fade away automatically, say, over 5 seconds when your load operation is complete) -- and
it normally appears at the lower right of the screen, out of the way. You can put any controls or user controls you want in a notification window, including a progress bar. As a matter of fact, I'm using notification windows in my current VSTO
Excel 2010 ribbon project:

(an example of implementing notification windows is at http://www.codeproject.com/KB/cs/diffusedialog.aspx )
A helpful rule of thumb from usability experts is to use the Hourglass cursor for operations requiring between 1 and about 7 seconds, and a progress bar for operations requiring > 7 seconds.
Good luck!
Anonymous9748