A lot of programs produce reports in specially formatted files that may sometime have dat extension. You cannot probably find exact answer on internet when looking for a dat to xls converters, however you may try direct import to MS Excel.
You can do that by manually opening your .dat file in Excel using the File ► Open function. Even if Excel does not recognize your format, it may still attempt to import the data. You just need to tweak the settings of separators etc. The result may not be perfect, but for a lot of formats it should be enough.Open DAT file Open XLS file