well it's really quite simple...
1) open excel
2) enter the dates of 2010 into column A
3) Enter the corresponding price of whatever instrument you are doing this for into column B
4) Enter the formula =LN(B2/B1) into cell C2. Drag down all rows
5) Enter the formula =WEEKDAY(A2) into cell D2. Drag down all rows
6) create a pivot table of columns C & D with RowLabels as col D and Values as average of col C
I took the trouble of doing this for the FTSE in 2010 for you. Turns out Mondays are the best day to enter trades and Fridays are worst