MySQL 4.1 causes some problems, 4.0 doesnt
PHP5 is totally untested by Tiki Developers
PATH_TRANSLATED will probably needs some fixes like running on the IIS server does. See that IIS guide from InstallTiki to see what I talk about. Could be the first PHP5 or Apache setup problem.
1.9 is development code hence the RC (Release Candidate) flag. 1.8.4 is the latest stable release.