Its impossible for me to guess what makes your 'local websites' unique form each other. That is particularly true if they are dynamic rather than static.
You should look in the error logs (I am assuming the errors in your first post were 'display errors'). Some third party scripts have custom error logs, I don't know if this is true of Joomla - so I would check with them.
The rules/syntax changes with each PHP release. You say 'websites' - but I don't know if they are all Joomla powered. If these are things you did not code, you should check with the authors/developers.
Apparently based on previous comments here and after doing some searching Joomla has some problems with PHP 5.4. Re-installing with XAMPP 1.7.7 (which has PHP 5.3.
might be a good solution for you.