Wing Commander Fowler,
You would use a RAID Controller Card. Anand Tech had an excellent article on RAID Controllers a couple of years ago. The info explaining the Theory is well worth the read:
IDE RAID Comparison
With the current reliability of Hard Drives, it is now worth going with RAID 0 (Stripping). Just make sure you keep up your backup routine.
With two drives, you want them to be matched for optimal performance. If you have a 60Gb ATA-100 7200rpm w/8Mb Cache and an 80Gb ATA-133 7200rpm w/8Mb Cache you will not have a speed issue, remember the 36 gallons per hour per drive, but you will be limited to the use of 60Gb per drive and your system would see it as one 120Gb Drive. Anand Tech goes into greater detail in the article. If you put a 5400rpm drive with a 7200Rpm drive, you will only get about double the thoughput of the 5400rpm drive, not the 7200rpm drive.
Take Care,
Richard