for downloading is the same as uploading! the question is, how long does it take for it to time out? have you tried smaller files?
the issue could be with http request where the setting in your web.config is set to a low number so when it reaches that number (seconds) it times out and you dont download!
also have you checked your log to see any errors being produced at:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\LOGS
for increasing timeout:
Note We recommend that you set the maxAllowedContentLength value
slightly larger than the maximum file upload size that you have
configured in SharePoint. If the maxAllowedContentLength value is
equal to or smaller than maximum file upload size that is configured
in SharePoint, users will not receive the error message that they are
exceeding the size limit if they try to upload a file size larger than
that specified by the administrator.
i know the above is not for 2010 but its very similar if not the same!
if you want 2010: