Trouble with #N/A trying to find averages

Hi I have attached a file to help explain my problem.
In sheet Teamdata I need to average the vlookup returns in columns N,P,R,T etc. Each day stats are added to the Database section so more and more columns will fill with numbers rather than the #N/A where there has been no game yet.
In column I, I'd like the average of the numbers in N,P,R,T etc. When I just try to average them all I obviously get a return of #N/A. Maybe it is possible to use column C's data,which tells how many games that team has played, in some kind of average function using column C's data as a variable.
I am sure there are many ways to do this, any help would be appreciated. I am on 2007 btw if that would make any difference. Thanks in advance Andy