Calculate Directory Size

I'm not sure if this is the right place for this query or not, but it does involve a bit of Pear DB and DB Pager. Here's my problem...hopefully someone can help, because I've no idea where to even start! I have a user database, with a table called Users, and fields as so: (it would be cool if this would work on both Linux and Windows) ------------------------------------------------------------- User DiskUsage (Mb) Quota (Mb) HomeDirectory ------------------------------------------------------------- jim 50 100 F:\users\jim \\ In Windows jim 50 100 /users/jim \\ In Linux ------------------------------------------------------------- The database wouldn't be shared between Windows and Linux, just 1 or the other. What I would like to be able to do is, press a button on a php page, and scan the (MySQL or ODBC through Pear DB) database, and for each user, calculate the size of their HomeDirectory, and Update the DiskUsage in the DB accordingly. I'm wondering tho how this would work with say 1000's of users each with several hundred Mb's or even several Gb's each. The users will have subfolders too, so the function would have to recurse the dirs. Is this even possible with PHP? I appreciate any help I can get on this, because its waaaaaay beyond me presently. Thanks Simon H