[dba-SQLServer] Ram use for queries

Is there any tool for seeing how much ram SQL Server requires to run a
specific query?  Does (or can) SQL Server use disk to handle that temporary
storage.  

I have queries to run against these huge tables which require 1/2 hour or
more to complete.  Trying to move up to servers running enterprise versions
of Windows 2003 and SQL Server and which would run 16 or more of ram would
be hugely expensive, however I can build raid 0 arrays of ram disks for a
"reasonable" price, ~$1600 for a 16gb drive.  Obviously 16gb is not big
enough to put the main databases on, they are up in the 100-200 gb size
range.  However I might be able to put the log files out there, or the
tempdb.  In fact I am reading about placing the tempdb files on ramdisk but
there are no metrics described for how big these things are.

Has anyone ever tried, seen or heard of this being done?  

John W. Colby
Colby Consulting
www.ColbyConsulting.com