To Upload large files you need to change a number of settings.

For details read: http://us2.php.net/manual/en/features.file-upload.php

In your php.ini set upload_max_filesize, post_max_size, and memory_limit 
to values larger then the largest file you want to upload.  You
may want to post_max_size to a value greater then upload_max_filesize,
since warnings created by going over this limit aren't catchable with an
error handler.

You'll also want to set UploadProgressMeter::$maxFileSize to the same value
as upload_max_filesize.  This value is in bytes, and is used to give the
browser a max upload size.