burner problems

I have a MSI CDRW 40x12x48 on Cel 500, 128 ram, 6gb hd, Win 98.
When I drag and drop my music files onto a cdr it works fine, but if i want to add more music to the ? empty cd it says I must have a cdrw.
I know u can do this with data, is there a way to do it with music files or do they need to be converted or am i doing the whole process incorrectly?