using sed with xml files part 2

I'm trying to replace a date in an XML file that has the format mm/dd/yyyy. I'm using the Unix date function to set up a variable with the current date but, when I try to replace the value in the XML file, the error message says it cannot be parsed. Here is the command I'm using

s_\(<service_date>\)[0-9/]*\(<\/service_date>\)_\1'$service'\2_

I would really appreciate any help - thanks

s_\(<service_date>\)[0-9]\{2\}/[0-9]\{2\}/[0-9]\{4\}\(</service_date>\)_\1$service\2_g

Thanks for your help vino - I really appreciate it