XML Spreadsheet files have a lot of formatting stuff in them that you would probably need to parse out. If you are using SSIS, I know that in .net you can open the xml spreadsheet and save it as a standard xls.
I imagine you can somehow do this in vbScript as well, but it is probably not nearly as easy.
I don't think you will be able to bulk insert this, unless you convert it to a standard xls file. I rarely So you'll either need to use DTS/SSIS to change the file, then import or just open it and do a good old 'save as' before doing a normal bulk insert.
Hope this helps,
Alex
Ignorance of certain subjects is a great part of wisdom