If you owned the game as a CD then you need a CD to play it. You can't just download it for free.
You can check if you purchased the game online at http://www.xbox.com:
- click on "My Account"
- click on "Billing History"
- enter your login credentials (you will end up at commerce.microsoft.com)
- click on "Transaction"
- adjust search criteria and click the "search" button.
There you should see something like "Street Fighter 4 AE: Xbox 360 Edition" as the description with a "Purchase" transaction type.
If it's there you should simply be able to download the game again either via xbox.com or directly from your Xbox.
I think this is the link to the game you're talking about:
However, if it's not an online purchase then you need the CD to play it again.