3/26/2008 -- Depending on the size of the files that you're trying to upload, there are several things that you can try.

First, make sure that SharePoint is configured properly for the maximum file size that will meet your needs. The default maximum file size for uploads in SharePoint is 50MB (with the absolute maximum at 2GB or 2,047MB). Make sure to adjust that number according to your needs. Also, try to increase the paging file on the server to at least 1GB and see if that helps.

If you're using URLscan on your server, you may have to update urlscan.ini to modify the value for MaxAllowedContentLength.
You may also want to experiment with the value of executionTimeout in the web.config file. Try setting it to a higher number in seconds, like 3,600 or even higher.

Another thing you can do is to ensure that your browser is properly configured to accept large files. What you need to do is configure Internet Explorer to increase the Send buffer when communicating with Winsock. By making this change, you'll be increasing network performance for the HTTP File Upload method. Making this change requires a registry hack.

Microsoft IT reportedly limits their SharePoint file upload size to 100MB. For some additional solutions and information on the above-mentioned registry hack, check out this blog post.