Decimal format

I have a custom list with autocalculate field (Number) then in sharepoint
designer I enter a xls datasource a dataview, and total sum like;

Header --> Work Hours
Line 1 --> Work1 1,20
Line 2 --> Work2 3,50
Line 3 --> Total 4,70

the first problem is that in the line 1 Hour I have NAN, because the output
format of the datasource is #,##0.00 (english number format) then I can't
convert in a number

The second problem is with the sum because $nodeset/@Hours containt a group
of nodes with 1,20 and 3,50 them I can't do this sum

I know that it's languajes insue, but I can't find the solution PLEASE HELP!!!