Only if they are networked or otherwise connected if you mean in real
time. If you instead mean you want to move large volumes of files back
and forth you can burn a CD, DVD or copy files to a external hard
drive which can be taken from one machine to another. If you PCs
support USB 2.0 and you have your BIOS set up to support it and the
feature is also supported by the external hard drive these days you
can now "hot swap" which means you don't have to reboot anymore. Just
a matter of plugging the external drive's power supply and plugging in
the USB cable. Some newer drives also support hot swap SATA drives.