Greetings,
I have been researching the same issue, and not happy with the answers. Yes, you can get a Town car (I have used Tiffany's Town Cars before with good luck), but it looks to be about a $75 charge from any Disney Resort to Universal. I have also heard that Mears runs a shuttle service for I believe about 12 dollars per person, but you would have to check on that one. If you are really adventurous, you could go catch the Lynx at Downtown Disney West side (public bus for a $1.25), but you would really need to investigate the route (http://golynx.com). I think route numbers 302 or 303 and it looks like it takes a while.
It is about 17 miles from the Downtown Disney area to Universal and is esimated to be a half hours drive. Either way it looks painful to me and a real source of contention. There should be a better means to get between these competing parks, as they are really so close to each other.
Regards,
James