Excel - chenge decimal places into comm

Dear Sir,

I am using Registered Copy of Excel - 2000, I had problem with Excel as follows :

when i type any number with decimal places it automatically change the decimal format into comma format i.e. if i type 5242.85 it will display the number 5242,85 It will affect to whole worksheet by default.

i checked the cell category, in Custom category by default type is General. But here it shows Standard. In Number category , it show all sample numbers in comma format i.e. 1234,10

I reinstalled office 2000, but it works same. So can u suggest me what the problem with Excel-2000.

Thanks

Raju Niphade