By default, the max content header length is set to 30mbytes in IIS 7. You need to adjust this number up to allow files larger the 30 Megabytes to be uploaded. Details can be found here. http://support.microsoft.com/kb/944981

Read all about it here: http://blogs.msdn.com/sharepoint/archive/2008/03/07/moss-2007-with-sp1-slipstream-officeserverwithsp1-exe-released.aspx

Gives you step by step directions for installing MOSS on Windows Server 2008 and provides other information. http://technet.microsoft.com/en-us/office/sharepointserver/bb735844.aspx

One of the better KB's I have seen. Thanks! http://support.microsoft.com/kb/936984