A 7200 RPM HD is worth getting, IMO, over a 5400 RPM drive. You'll see a noticable difference in performance.
As far as an ATA-100 interface vs. an ATA-66 interface, It's not worth it to buy an ATA-100 PCI card, you simply won't get much of a performance increase. On an ATA-66 bus, a 7200...