32 vs 64 bit SYSDIR - need some help/explanation

[Brummelchen]

myself actually works on 32bit - so all tools are working with $sysdir.

But i am not sure about 64bit.

is it "\system64" instead "\system32" or "\sysWOW64" found here?
http://forums.winamp.com/showthread....hreadid=269506

i write on a portable defragger which is available as x86 and x64.

contains $sysdir the correct path for both?

how to determine 32 or 64 bit?

WOW64???
http://forums.winamp.com/showthread....hreadid=237297

Application is for WinXP and Vista.

thx

PS registry in the work too, is this needed?
http://forums.winamp.com/showthread....hreadid=271710