Pub Poker League Table Help

Hiya all
Only just found this forum after trying for weeks to workout the right formula for this league table, hopefully somebody on here can help.

I run a pub poker league, and what i need is automated table that works out the leaderboard, but by only adding their top 20 scores out of all their score's entered.
So on the first page i will have all the names of the players and each week i will enter their score for that week, upto i think around 45 weeks in the year. While on the 2nd page a table will form working out the leaders of the game by adding their top 20 score's ONLY out of the possible 45 weeks. Also a average of their top 20 score's would be a nice addidtion to the table if this can be achieved.

If anyone can help and would like to contact me personally, please feel free to email me at whirlers@blueyonder.co.uk, or if you need anymore info
Any help is much appreciated
Thx
Graham