If it's not expected to get big then keeping your data and log files on the same disk should be fine. Just keep them off your OS drive. From your config (1 machine, 2 drives) I'm assuming a small database.
If your db is expected to get bigger (gb+) and you want the utmost performance, you'd want to have multiple drives (not just partitions) raided on a good quality san (can get very expensive).
Ideally, what you want is to minimize IO contention on your database. I'd keep tempdb, the data and logs all on separate drives and I wouldn't even use the OS drive for any of the databases including master, msdb...