generalzing the xpathexpression using variables

hi to all,

i am new to this forum and also new to xml too…

i have an xml query to selct alist of values…

XmlNodeList nl=doc.SelectNodes("//group[@group_name=‘Friends’]/@group_name")

it can select only the node having value as Friends

i want to generalise the query by substituting a variable in palce of ‘Friends’

how can i do …
pls guide me