How can I connect 1 1/2 pvc drain pipe (from washing machine) into an existing old 1 1/4 metal pipe?

Probably a flexible coupling like this one: http://www.fernco.com/sites/default/files/dimensio... You'll want to take OD measurements of both pipes because this clamps over the outside. The guys at the local plumbing supply store told me that it was code around here (VT) to use these couplings whenever you go from one pipe material to another.

You can probably find a swag piece to go from copper to PVC that you can use, then add a 1 1/2 x 1 1/4 reducer to fit your drain pipe. You should realize that having a restriction in the bottom of the washer drain line will cause a slight back-up in the drain pipe.

challenging stuff. try searching using yahoo and bing. just that could actually help!