Just like the title says. I'm trying to put on some muscle mass. No, not a huge amount, but enough that I got some bulking supplements ( At Large Nutrition - Maximum Mass Supplement Stack ).

Anyhow - I've gotten into the routine of lifting hard on one day for 30 minutes to an hour, then the next day working out on my elliptical machine pretty intensely for 30-40 minutes or so, then going back to weights the next day, etc... just alternating back and forth with no real 'off' day.

Is doing cardio counterproductive for my weight lifting or is it just 'ok' or maybe it's even a good idea?

Everywhere I read says workout one day, rest the next - but I wonder if they just mean 'rest' as in 'do not lift', but other aerobic type activities are fine/good?

yes when they mention rest they refer to not lifting weights. Eitherway, you should have at least one day of the week were there is no weights or cardio involved.

Cardio is fine, just get an estimate on how many calories you're burning and even it up by intaking more calories. No matter what you have to intake more calories than you burn in order to gain weight.