Takayuki Miyoshi on "[Plugin: Contact Form 7] File uploading not working for uploads >1mb"

Note: I'm using CF7 2.4.6 with WP 3.0.4

Do you have any reason to continue using those old versions?

There are PHP settings relating to the size of uploading files. Check the settings on your server.

http://www.php.net/manual/en/features.file-upload.common-pitfalls.php