Using Flash Memory (SD, SDHC, SD II, XD, MMC, ETC) as VISTA Ready boost

I am trying to figure out if there are SD cards (or any other format really) that will work with windows vista’s ready boost function, the function that uses USB flash drives as system memory to give them a boost

the reason i ask is that ive got a toshiba laptop with a built in card reader, and if this will work as ready boost, then i am going to use a large (2GB+) SD card to boost my systems boot speeds and such

Any help would be appreciated, and really if anyone knows what are the minimum required Read/Write speeds for ready boost to work, because i have seen SD cards with read 21mb/s, write 15mb/s and such