By default a file with size 50 MB can be uploaded to a SharepOint Document Library (WSS 3.0), but it can be configured to support upto 2,048 MB (2GB).

One can use following steps to configure maximum file size allowed in SharePoint:

1. Click Start, point to All Programs, point to Administrative Tools, and then click SharePoint Central Administration.

2. Under Virtual Server Configuration, click Configure virtual server settings.

3. On the Virtual Server List page, click the virtual server that you want to change.

3. On the Virtual Server Settings page, under Virtual Server Management, click Virtual server general settings.

4. Under Maximum upload size, type the maximum file size in megabytes that you want, and then click OK. You can specify a maximum file size up to 2,047 megabytes.

After doing this configuration changes in SharePoint, you also need to increase the connection time-out setting in IIS. For complete details please refer to following help post from Microsoft:

http://support.microsoft.com/kb/925083