Drive C is partitioned and the second partition (F) carries all my data.
Its
backed up, but I'd like, if possible to format C without interfering
with F,
reinstalling Win 7 on C. Is that possible?

Without any problems at all.
During the installation when you are asked to select the partition you
wish to install the operating system on you should have the format
option.

The format will be performed on the selected partition, NOT the
selected drive.

/ Ani