The currency symbol is specified by your systems internationalisation configuration, so if your computer 'thinks' it is in a dollar country (or hasn't been set up_ it will show a $ symbol. If its incorrect set the symbol via start | control panel | internationalisation
if you don't want a currency symbol: as myle suggests use a general number format. Althgough I'd suggest
NewFieldName:Format([filename],"#,##0.00") will give a currency style formatting.
bear in mind though that if you are displaying currency information that some beancounters get very upset if the totals & subtotals don't tally exactly. so you may need to use something like fix(myvar,nodecimals) to ensure that the sum of the rows equals the total