The key question is whether your ODBC client application -- the thing that's going to use the data -- is 32-bit or 64-bit. 64-bit Windows 7 supports both 32-bit and 64-bit applications. 32-bit applications can only use 32-bit drivers; 64-bit applications can only use 64-bit drivers.
Once you've figured that part out, you have to install a matching 32-bit or 64-bit driver for MySQL, and configure it with the right Administrator. The 32-bit Administrator is counterintuitively found at C:\Windows\SysWow64\odbcad32.exe, and the 64-bit Administrator is likewise counterintuitively found at C:\Windows\System32\odbcad32.exe.
Note that for added fun, Microsoft's ODBC driver manager (the MDAC) has a bug in that it shows 32-bit User DSNs to 64-bit client tools (including the Administrator), and it shows 64-bit User DSNs to 32-bit client tools (again, including the Administrator) -- even though these mis-matches cannot work together. For this reason, I strongly recommend using only System DSNs in any environment that may have a mix of 32-bit and 64-bit drivers/DSNs.