How to download minecraft snapshots:

1. Open new tab
2. Go into the address bar
3. Type in www.minecraftforums.net/
4. Wait for the page to load
5. Scroll to where it says snapshot updated to (whatever the latests snapshot is)
6. Click on the client link
7. Save the minecraft.jar that is automatically downloaded
8. Go into start
9. Go into the search bar
10. Type in "%appdata%
11. Hit enter
12. Click roaming
13. Click .minecraft
14. Click bin
15. Right click the file titled "minecraft"
16. Click cut
17. Make a new folder
18. Paste the file in
19. Go to downloads
20. Find the minecraft.jar you downloaded from www.minecraftforums.net
21. Right click
22. Cut
23. Paste into bin
24. X out all folders
25. Run minecraft
26. Have fun!

Shorter version:

1. Go to minecraft forums
2. Find the snapshot section and download the client
3. Save it
4. Get the old minecraft.jar from bin, cut it, and paste is into another folder
5. Paste the downloaded minecraft.jar into bin

DONE!!!