calculating kilobytes

hi first of all i think this is a great community here :) now to the point... i need a script. it should work on safe mode php so it should be as simple as possible. it should calculate all the file sizes in the directory that it is in and in the subdirectories also (only 1 level subdirectories). it should echo the total size of the uploaded files. then it should take the filesize and substract it from 25 megabytes. that is the limit on this server. then it should echo the result (the maximum number of kilobytes that can still fit on this account). unfortunately i have insuffitient knowlege to do it miself. i just want to thank anyone who can help me. if you want to send it to my email then its liberache@hot.ee . or you can just write it here. thank you :)