InstallShield iss error

[sajiby3k]

I know how to create and use "iss" file in installshield setup. But i look at some disgusting configuration of iss file. Say for example power dvd 6

[{6811CAA0-BF12-11D4-9EA1-0050BAE317E1}-SdAskDestPath-0]
szDir=C:\Program Files\CyberLink\PowerDVD
Result=1

szDir is the directory where powerdvd will install. But i want to setup powerdvd in the the drive where my windows is install. In other setup like inno setup, nsis the software usually install in the "program files" where the windows is installed. I tried to use "%ProgramFiles%\CyberLink\PowerDVD", but installshiled doesn't recognize windows environmental variables. So, is there any way of installing software silently by determining in which drive windows is installed