Listening to music is the only possible memory intensive application
you've mentioned. After loading whatever window manager or desktop
environment you choose, even with one as bloated as KDE, I'd think
512M would be quite sufficient -- for playing music files. If you
use OOo for writing, that will consume some RAM, also.
As for IDE vs. SATA, that is going to depend upon the motherboard
chipset more than the drive. You can get faster speeds with SATA
than IDE, but support for SATA in the Linux kernel is still developing,
so I'd read Jeff Garzik's Serial ATA (SATA) for Linux reports
And before you upgrade, make sure all your hardware is supported in the
Linux kernel you'll be running.
I have 2G of memory, and can't hardly use 25% of it in Slackware until
I launch Windoze in QEMU and run Adobe InDesign and Photoshop. Start
using GKrellM on your desktop and see what apps you run take CPU, which
take RAM, and which take your hard drive to the test.