While having multiple templates in multiple folders is generally not a great idea, in this case you could:

have the template, when it is used to create a new file, use DocumentNew to pull in your spreadsheet from the current folder. To get the current folder (i.e. the folder the template dotm file is in) use:

AttachedTemplate.Path & "\"

therefore to point to a xls file in the same folder:
AttachedTemplate.Path & "\test.xls"