I took my Red Hat 8.0 CD1, typed "linux rescue", went into the shell, did a "dd if=/dev/hda of=/dev/hdb bs=512", went shopping, came back, made the new drive the master, booted.
Worked perfectly. Then I just went into Partition Magic and resized the partitions the way I wanted, and reformatted the old drive (actually, I converted it to FAT32 so I can see it from both OSes, and I didn't lose any files just in case something was strange.)
Like windexcowboy said, the drive is quiter when reading, but mine at least makes more noise just sitting there than my old one did (the difference between 7200 RPM and 3600 RPM perhaps.)
Now I'm looking at a new motherboard, CPU, RAM, and video card.