I am not sure it can be done with Series 1 Tivos, but both my Series 2 boxes (HR10-250 and S3) allow you to set a remote address so that a given remote will control only one of the Tivo boxes.
Check your System Information and see whether it shows a Remote Address. If it does, it will probably show a current address of zero, which is the universal address. Then check your manuel to see whether it shows instructions for changing the remote address.
Assuming that you can change the address, you can either just set a different one on a second remote or purchase one of the newer remotes from Tivo, which contain a switch to select the DVR you want to control.
RSS