Forms and Formulas

hello all,
i looking to create a form or input box that will place data in a specific cell insted of a the row after the last data row

also i am looking to make a formula that will average data of one column based on the criteria of another column for intences
1 _________ 10
2 _________ 8
3 _________ 6
2 _________ 10
3 _________ 10
4 _________ 8

if i wanted the average of the second column base on the critera of the first, so if i wanted the know the average of the 3's in colmun 1 the anwser would be 8

help chris