The drives store 5x1011 bytes of data each. But the operating system counts a gigabyte as 230, not 109. The latter is 1,000,000,000 and the former is 1,073,741,824.
So, my 500 GB drive only stores 450 GB. *shrug*
But even so, if you count the other hard drives that are connected to the system, the end total still ends up being over 1 TB of total on-line storage:
Drive 0: 150 GB
Drive 1: 150 GB
Drive 2: 450 GB
External: 450 GB
Total: 1200 GB
It "only" took the computer some three hours to format the new drive once I got it installed, and copying the data from the old EIDE drive it replaced took 40 minutes.
Next upgrade: memory. Crucial.com has some pretty good prices on 100%-guaranteed-to-work memory, and I've had good results from using their products in the past, so that's the way I'll go. I just need to decide if I want 2 GB or 4 GB. Well, you can't go wrong with maxing out your RAM, I always say. Programs aren't going to spontaneously start getting smaller anytime soon. Windows Vista runs acceptably in 512 MB of RAM, but most windowed operating systems are memory hogs and MS products set the standard for that--1 GB of RAM is pretty much required for anything better than baseline performance, and 2 or 4 GB is vastly superior to 1 GB.
People always ask me if adding memory will speed up their computers. My answer used to be "no", back when the OS was 85-128k worth of machine code--but now it's hundreds of megabytes of compiled C++. My answer is different now.
More memory won't necessarily help your machine boot any faster, but it will limit the machine's need to use virtual memory. These days, I always strongly recommend that people max out the RAM capacity of their computers. If that's not economically possible, then at least try to run 2-4x the "minimum recommended" RAM of your OS.
So really, I have no excuse. Guess I ought to get cracking.