For more information I would see this JQS help article
JQS is enabled by default in Windows XP and Windows 2000 operating systems and JQS is not necessary on Windows Vista or Windows 7 as both offer their own pre-loading mechanisms. A process called jqs.exe will run in the background in order to allow quick startup. jqs.exe will be loaded after a Windows restart. Instructions on how to disable the JQS and the jqs.exe process are below.
As far as I can tell, Oracle sees no need for it on Vista and 7. I don't believe it's possible to enable it on either OS. Interestingly enough, the help page provides documentation on how to turn JQS off on Windows 7/Vista, but not on.
As for Vista/7's pre-loading mechanism, it appears that, unfortunately, there's no way to specify programs to cache. It's all done automatically.
As for ramdisks, as Journeyman Geek mentioned, there are tons of options such as AMD Ramdisk or Dataram's Ramdisk.