oscommerce digital products download problem

hi , i am a individual freelancer. i have a problem in digital download that is size of file. if file to be download is less than 2 mb everything works fine. but bigger size than size of downloaded file is 2kb only means not downloaded properly. the files can be as large as 600-700 mb as this are movie files. i will pay $10 via paypal to right helping person. who ever give me first the right solution will get this $10 amount. please suggest your solution in PM and i inform that i am not using super download shop contribution. thanks ~ phpmysqlguru