There's nothing wrong with doing it that way at all, at least it's safe. Accidentally installing Windows on the wrong drive and having to do it all over again wouldn't be fun. The Windows 7 installer does do a good job of showing which drive is which, as it lists the sizes of each drive and where they're installed (ie drive 0, drive 1 etc.) but there's nothing wrong with doing that method either. In a lot of cases, especially when troubleshooting issues, OS reinstalls are actually recommended to be done in this manner.