R help - May 2008 - individual analysis

Dear R-community,

I'm looking forward to analyse the results statistically
for a new medical diagnostic tool. The aim is to know whether a given  
subject is different from the mean or distribution of a population of  
controls for one continuous variable (a neuro-imaging results which  
can be quantified).

Does anyone knwows which test is appropriate for such an individual  
analysis ? Which package is necessary to perform the analysis ?

Thanks a lot for your help,

Julien