Can I attach a remote CD/DVD player to my macbook pro 3.1?

You won’t normally be able to use Apple’s USB SuperDrive with it. If you don’t already have one, buy a non-Apple optical drive.

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Did I understand this correctly: you are trying to get Snow Leopard? It is not available via download - you can buy a retail DVD at the online Apple store. And, if it were available or you want any OS later than Snow leopard, you could simply download it to your computer from the app store - no need for a DVD drive.

Frankly, I do not know if an external drive will work for a direct/via USB installation on an older device. I know they do now. However, any external DVD drive/burner that says it is compatible with Macs should do it. You don't need to "download"; you should load the DVD into the burner and then boot up the laptop holding the C key immediately after the chime. That should boot it from the DVD. If that does not work, try plugging in the drive with the DVD in it and then booting up your laptop. If the DVD shows on the desktop, you can open it and install from there.