Finding Median Value

Hi,

I have looked all over the web to try to find some very basic / simple explanations of how to get a median value from a group of records in a table but with no luck

the problem i am having is that all the information i find is always centered around getting a median using every single row in the table. except i have groups of data in the table and want to work out a median for each group. the group is identified by 4 different columns (the 5th column is what i want to get the median on but for each group not the entire table) and i want to produce a resulting table that has 1 row for each group and therefore contains the median value for the group instead of the individual numbers that it currently has. e.g. the current table is like this

column1 column2 column3 column 4 column5(median of this)

value 1 value 2 value 3 value 4 1.2
value 1 value 2 value 3 value 4 1.0
value 1 value 2 value 3 value 4 1.5
value 2 value 3 value 4 value 5 0.2
value 2 value 3 value 4 value 5 0.4
etc...

and i need a query to get the results to show like this

column1 column2 column3 column 4 column5

value 1 value 2 value 3 value 4 1.0
value 2 value 3 value 4 value 5 0.3
etc...

This is driving me crazy and i will be very helpful if anyone can help

the statement i need to add it to is:

select pat_demid, pat_lastname, meas_gendate, meas_id, test_gendate, avg(srtot)as meansrtot, avg(sreff)as meansreff, avg(BFRaw)as BF_Rawmean, avg(BFTGV)as BF_TGVmean, count(srtot)as countsrtot, count(sreff)as countsreff
from bodyparametersf
where (srtot is not null) OR (sreff is not null)
group by pat_demid, pat_lastname, meas_gendate, meas_id, test_gendate

thanks very much