Internet Explorer has a file download limit of 4GB (2 GB on IE6). Firefox does not have this problem (haven\'t tested safari yet) (More info here: http://support.microsoft.com/
What about saying "We recommend that you install Free Download Manager to download this file. You will have the added benefit of being able to resume the file and accelerate the download."
Personally I never download anything using the built in browser download tool unless I have to (e.g. Gmail attachments)