the %ProgramFiles% variable

Hello,

I want to use the %ProgramFiles% variable in a Sys.setenv (R 2.7.2,  
Windows) but it always seems to get handled literally. For instance,  
in cmd.exe I get what I want


C:\Documents and Settings\user>echo %ProgramFiles%
C:\Program Files


but in R


 > system("echo %ProgramFiles%")
%ProgramFiles%


nope. Is there a way to use %ProgramFIles% or get the corresponding  
path?

Thanks,
Kjell