I wouldn't worry:
Prepare for Windows Vistaâ„¢ Today
Since the days of Windows 3.11, Trolltech has a proven track record of remaining at the leading edge of development on the Windows platform. Trolltech’s continuing goal is to ensure that Qt applications created today will always remain current. Qt future-proofs your applications, freeing you to focus on value-adding innovation.
from http://www.trolltech.com/pdf/Qt_Windows_DS_A4.pdf