1. If you have any money, lend me some.
2. If you have some money, lend me some.
(Can we use both expressions? In the if clause, 'any' is used, I know. What is the difference between them if both are OK?)
3. You can't do everything.
4. You can't do anything.
5. You can do nothing.
(What is the difference among them? I think #4 is the same as #5. What about #3? What is the difference?)
1 & 2 -- both are about the same. The only problem with the second one is that "some" appears twice in the same sentence.
You're right that 4 & 5 are the same and that 3 is different.
3 implies that, even though a person tries, he or she cannot do every single thing in the world.
4 & 5 imply that "you" are unable to do anything correctly.