Hello Doc,
Thank you very much for the detailed and understandable (for a nontechie person) reply.
You're welcome.

I wanted to ask you some follow-up questions:
What steps do I need to take to replace the hard drive?
Physically? In most cases (with a laptop), you simply remove a screw or two, slide out the old hard drive, slide in the new, and then replace the screws. But, that's the easy part. Installing/configuring the Operating System (and then updating it), installing/testing all of the required drivers, installing & updating all the anti-virus/-malware, etc. can take hours. It's not that it's really hard to do, (in most cases), it just tedious.
Is that something that is sold in office/electronics stores, such as Best Buy?
Yes. Or online at places such as Newegg.com, TigerDirect.com, etc.
Should I look for a particular brand/model/make?
Seagate and Western Digital are both good. What you really need to look for is the same type such as SATA or IDE etc. As far as the capacity goes, buy as much as you can afford.
I am not sure if these terms are correct, as I have never had to replace a hd myself.
Do you have a 'geeky' friend close by that would be willing to lend a helping hand?
My second question is about the bootup partition on the hd: is this partition something I have to set up when I replace the hd or does it exist on the hd at the time I install it?
Hard drives come 'bare', (so that you can install any Operating System you like). And yes, you (someone) will have to completely 'set it up'.
About the OS: do you recommend that I use a particular OS? My mom has win XP home edition on her desktop pc (a dell), and I used to have win vista home edition on the toshiba laptop. I do not have any reinstallation disks for the win vista other than the recovery disks. Mom has her reinstallation disks for the win xp home edition, including the disks for all drivers, utilities, tools, etc. I wonder if I can use one of these options above (recovery/reinstallation disks) instead of buying a new OS disk from an office/electronics store.
Recommend installing the same Operating System (Vista). The reason is simply because of the drivers you'll need to get things like Audio, Video, Touchpad, Ports (USB, etc.), webcam (if any), etc., all working once again. Since all of these items were (presumably) working before, we know that Toshiba has all of the necessary drivers available for your particular laptop and Windows Vista.
Thank you very much again,
Ellie a/k/a Paperclip
In your particular case, you might consider simply taking your "Toshiba Satellite laptop" and your "win vista recovery disks" to someone like Best Buy. That is unless you have a 'geeky' sort of friend that would be willing to help.