I am not sure how well PostgreSQL data works with ram disk. In linux there are howtos that fully describes how ramdisk behave and how to configure them. There's even one howto in particular to describes the mechanics of how, during the boot up process, for a time a ramdisk is mounted as the root directory. You'll also have to investigating using filesystems other than minix.. which I am not sure if it will meet your needs (filename length limits and what out).. e2fs or something else will have to replace minix for your ramdisk usage. Lilo howtos will show you how to set the initial maximum size of a ram-disk partition. Etc etc.
