So you have an Excel 2007 spreadsheet that you want to convert into a SharePoint List (WSS 3.0 or MOSS). So you use the "Create" button on the website and you select "import spreadsheet". So Exel opens on your machine (you are using Windows/IE, right?) and asks you to identify the range of cells. So you do that. So Excel thinks for a while and says "Method 'Post' of object 'IOWSPostData' failed". So then what?
So then you need...
The Sean Blog : Uploading Spreadsheets into SharePoint Lists
You have to fix a bug in the code of the export add-on from Microsoft -- yes, "the greatest company in the world", and you have to fix their code to export from one of their products to another one of their products. Sean shows you how with pretty pictures. [The solution isn't original with him -- see his post -- but I found the screenshots helpful.]
He also mentions an add-on that permits two-way synchronization between Excel spreadsheets and SharePoint lists. I haven't tried that.