and infact if your computer is slow under traditional, you're unlikely to see major performance boosts from SSD.
Cobblers... I recently changed the 5400rpm drive in my wife's 4yr old MacBook Pro for an SSD and it went like stink. Boot time reduced by 75%, applications open almost instantly. For non-power users who don't spank the CPU/RAM all the time and require huge amounts of storage space an SSD is the most cost-effective way to bring an older laptop back to life. It easily surpassed current MacBook Pro models with traditional hard discs in terms of day to day performance. All this despite the fact that the MBP SATA controller is limited to SATA1 speeds.
If the SSD is a little too pricey, don't bother with 7200rpm. Look at the 10,000rpm VelociRaptor drives, or the Momentus XT combo drives; both destroy conventional 7200rpm discs and you can have 500GB for well under a ton.