After looking at an example On this site. About a third of the way down is the code for saving the file.
http://www.oooforum.org/forum/viewtopic.phtml?t=4996
First of all you know your file path is for a XP style system correct ?
According to the example you seem to be skipping a step.
The example shows :
cFile = "C:\Documents and Settings\dbrewer\Desktop\MyCalc"
cURL = ConvertToURL( cFile + ".xls" )
oDoc.storeToURL( cURL, Array( MakePropertyValue( "FilterName", "MS Excel 97" ) ) )
Hope this helps.