you will need:
FireFox
Cheat Engine 5.5

1) Open farmville and cheat engine
2) change your value type to double
3) type in you money
4) first scan
5) double click on the money you see that is yours on the left (without the ... so if you have 3000 make sure it dosent have 3000.242 or something like that)
6) Do the same with exp
7) Change you value to 500000000 for both of them
8) buy a hay bale
9) make sure you dont buy anything less than your original money
10) have fun