Hi,
I have the same issue. German .xls file with XINTZINSFUSS formula on english
version of Excel2003. Anyway, I have the Microsoft Office 2003 Multi-lingual
User Interface Pack (German MUI) installed and even did the update to Service
Pack 1 for that which is available on the support.microsoft.com page.
Still, that does not do the trick. It appears that this formula was
unfortunately not translated and since we are talking about Excel 2003 I do
not expect a translation for this.

As a workaround you can do a global find and replace as the German
XINTZINSFUSS is the equivalent of the english XIRR.

I am using a company PC and since i like my job I will not install any 3rd
party tools which convert or upgrade my Excel. The risk is just too big.

OH