filesize() and mime_content_type()

Is there anything special you need to do to utilize these functions? The former says it's available in versions 4 and 5 while the latter states that it's available in versions >= 4.3 and 5 (although is deprecated). I'm currently running PHP version 4.3.11 on a Windows NT box. Based on both those pieces of information, it seems like I should be able to make use of these 2 functions. However, whenever I run the script I wrote doing so, I get the errors Fatal error: Call to undefined function: mime_content_type() and Fatal error: Call to undefined function: filesize() Why? They are both internal PHP functions and are both available (or should be available) in the version of PHP that I am running. What's going on? thnx, Chris