They do have a 1-day 2-park ticket. I'm not sure of the price, but I think it is in the $80 range.
Actually a co-worker asked me if you can do both parks in one day. You can, but if it is your first time to either park, it will be very, very tough. I doubt you would enjoy your stay that much. There is a whole lot of walking and rushing around, especially with the reduced park hours this time of year.
But then again, if you aren't into thrill rides, you could spend most of the day at Universal Studios, do a lot by 3pm, and then jump to IOA and just do Spiderman, JP River Adventure, Posideons Fury, and Cat in the Hat. If IOA closes at 7 or 8, you should be able to hit those 4 rides and still have a few moments to relax.
It is tough, but DW and I have been able to do it.