strings

Hi all,
I have a string.In that part,I want some part of the striong to be static and some part to be chamged.
 
EG:
/334-17_Compound_Medication_5_24_2010_12_1_54.xml ;
Inthis string Compound Medication should remain same whereas the rest can be changed.What is the procedure to do that.
Thanks It's Urgent.