xsl formating string

I have a xml file that I has strings in it.  I want to
do so sort of if logic that says if it is "C1" format
with blue text if it is "U1" format it with underline.
 Then if it is "0" I want to concatenate a .0 on the
end of that how can that be done?  How can I do these
things.  I know that I will probably use an xsl:if 
but I am not sure what the snytax is with comparing
strings.  Can someone give me a sample code of how
this would be done? Thanks!

Josh

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