not really, since most hard drives are the same phyisical size, only bigger ones are just denser (store more per square inch)
if the Hard Drive is a 7200 RPM, or faster than your current hard drive, it will eat up a bit more electricity. takes more energy to spin stuff faster.
how much? I know not. look at the hard drive's documentations (maybe your toshiba has the specs in the manual)
sometimes this info is on the box.
hard drives aren't the main power user, though they do use some, as they aren't on all the time. they only use power, to spin the disk up, i.e. upon reads and writes, and before and after those. after it is inactive, some go into sleep mode (power management setting), where they take almost no power, but take a bit of time to wake up.
the main power consumers, in a laptop, are the Monitor, keyboard, and the CPU and RAM, as well as video chipset. those are on all the time, and drain batteries faster than a Gameboy. not as fast as a Game gear, though.
there are a variety of helpers for laptops and power, like solar power generator, and foot powered recharger, that you may be interested in.
also, consider an AC adaptor, this will mean you need to use outlets, but you shouldn't be walking around while typing, of course. a car AC adaptor should also be available.
these save batteries, by using other power sources.