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.
Most laptop hard drives don't run nearly as fast their deskop counterparts, usually at only 4200RPM. IBM's travelstar HDs (the ferarris of laptop HDs) do 5400, but those are pretty expensive. I've yet to see a 7200RPM laptop HD.
All these parts are engineered to get the most battery life out of your laptop. If it didn't, it'd defeat the purpose of mobility, right? If anything, you may find the life extended, as better power management techniques come about.
Besides, you have a portege, which is Toshiba's premier mobility unit (I almost bought one, opted for a thinkpad instead). Everything in it is optimized for extended battery life anyway. And I think there's a BIOS function (along with the default windows configurations) to maximize the life.
Actually, the display can be the biggest battery hog on a lap top. But as stated above, most are optimized for extended battery use. Efficient use of power is a real problem all across the board in home and mobile computers. From a physics point of view, if we knew how to tap into the power of the atom efficiently, we could probably run a city on a 9v battery.