In Star Trek: First Contact, once the Enterprise's crew found out that the Borg were on board, could they have beamed the Borg off the Enterprise out into outer space, or do the Borg have the capability to block transporter beams?
In VOY: Dark Frontier, the crew stage attempt to beam some Borg off the bridge (in a simulation). This proves impossible because individual Borg are able to inhibit transport.
CHAKOTAY: Beam them out of here.
PARIS: I can't get a lock. They've adapted to our transport frequencies.
CHAKOTAY: Computer, freeze programme, both holodecks. What happened?
Moving (way) down the canon scale, in Star Trek: Online - Khitomer Crisis, a crewman is capable of beaming some Borg into the pattern buffer, then rematerialising them next to a hull breach, to be jettisoned into space. This only seems to work because the Borg are seriously malfunctioning.