I want to use a 1998 S70 for a couple of months to drive to work about 50 miles per day. The car has no compression on cylinder #1 but otherwise runs O.K. Is there any chance of ruining the motor driving it that way?

 

Yes. But its already ruined. You will likely ruin the cat too.

 

Why will it ruin the cat?

 

you will be dumping unburnt fuel into the exhaust which will eventually coke up the cells in the cat. Does the car run differently if you disconnect the fuel injector lead for that cylinder? (no compression in one cylinder suggests a burnt valve )

 

Disconnect the wiring to injector #1.

Motor is already ruined. Valve probably broken. Keep an eye on the oil level.