One interesting behaviour on 64-bit systems I saw today is how applications are run, and the fact that two command prompts are available (32 & 64 bit).
"Windows gets around these issues by offering two command prompts: one 64-bit and one 32-bit. Environment variables are set according to which command environment is being used.
For example, if you open a command prompt by entering the CMD.EXE command at the Run prompt, Windows will open a 64-bit command prompt. In most cases, the %ProgramFiles% environment variable for the command environment will be set to C:\Program Files. If you run a script, the script can interact with 64-bit applications, but not with 32-bit apps.
On the flip side, if you enter the C:\Windows\SysWOW64\cmd.exe command at the run prompt, you'll be running a 32-bit command prompt. In that case, the %ProgramFiles% environment variable will be set to C:\Program Files (x86). "
The key issue to remember here is that c:\program files should not be used for 32-bit apps or 32-bit COM+ components. Use c:\program files (x86) instead.