I use 32-bit explorer in 64-bit Vista because of a few problems that use 32-bit explorer extensions and therefore don't work in the default 64-bit explorer. So I call the explorer.exe in the SysWOW64 directory (confusingly, the apps in the SysWOW64 directory are 32-bit apps).
%systemroot%\SysWOW64\explorer.exe /separate /n,/select,%HOME%
%HOME% doesn't seem to exist prior to Vista/2008. Just replace that with whatever directory you want explorer.exe to start in. Of course if you're not using 32-bit explorer on a 64-bit system or if you are on a 32-bit system, you need something like:
%systemroot\explorer.exe /separate /n,/select,%HOME%
I also use this shortcut to launch the 64-bit Explorer (there are a few explorer extensions on my machine that are 64-bit only!)