[man]unlink/man is the delete command. I see no reason why it shouldn't work on win2K ...
Do a condition check with [man]is_writable/man previous to your unlink() call ... maybe that's the problem. Unlike win98, windoze 2000 has file permissions ...
The alternatives I can think of would be to use shell commands via [man]shell_exec/man, [man]passthru/man, or backticks, etc...
HTH,