Hi,
FlexCel 5.1 for VCL doesn't currently print, this is scheduled for 5.2 (which is already in internal beta testing).Right now, to natively print a sheet you would have to use FlexCel 3.6 (which can be installed side by side with 5.1) and use FlexCelGrid to print. The XlsViewer demo in the 3.6 distribution shows how to do it.
As said, native printing is coming soon to FlexCel 5, but it isn't available right now.
Regards,
Adrian.