Question: On OS from win 2000 or later (any language) can I assume that this path will always exists?
For example I know that on win xp in some languages the "Program Files" directory have a different name.
So is it true for the System32 folder?

Thanks.
Ohad.

Answer: 
You definitely cannot assume that: Windows could be installed on a different drive letter, or in a different directory. On a previous work PC Windows was installed in D:\WINNT, for example.

The short answer is to use the API call GetSystemDirectory(), which will return the path you are after.

The longer answer is to ask: do you really need to know this? If you're using it to copy files into the Windows directory, I'd suggest you ask if you really want to do this. Copying into the Windows directory is not encouraged, as you can mess up other applications very easily. If you're using the path to find DLLs, why not just rely on the OS to find the appropriate one without giving a path? If you're digging into bits of the OS files, consider: is that going to work in future? In general it's better to not explicitly poke around in the Windows directory if you want your program to work on future Windows versions.
Windows can be installed on a different harddrive and or in a different folder. Use the %windir% or %systemroot% environment variables to get you to the windows folder and append system32. Or use the %path% variable, it's usually the first entrance and the preferred method of searching for files such as dlls AFAIK. As per comments: don't rely too much on the system32 dir being the first item. I do think it's safe to assume it's in %path% somewhere though.