The best thing to do is to take the tram to the bottom of the hill (Universal City Walk) to the Subway Station (You can also take the subway to Hollywood Blvd, I.E> the the Walk of Fame) at the bottom of the hill. Take the Subway to the Metro Link station. Take the Metro Link to Angels Stadium in Anaheim and then the bus to Disneyland. For more detail direction look at these websites

LA Subway (MTA)

http://www.metro.net/default.asp

Metro Link (Train from LA to Disneyland)

http://www.metrolinktrains.com/

Bus to Disneyland (Orange County Transportation Authority)

http://www.octa.net/

There are also special buses and shuttle to and from Disneylan to Universal Studio.

Hope this help you.

I think if you are already at Universal, you might as well just take one of those bus shuttles. They are only $10-$15 per person and pick up often. A lot less walking involved and no more money than subway. Public bus will cost less, but a lot of walking and waiting involved.

If you are staying at a hotel, they can make a shuttle reservation for you.

one routing would be to take the Red Line for $1,25
to the 7th/Metro station then go to 7th/Flower and board Line 460 (it will cost you $2.50 more for this bus but will take you direct to Disneyland
(you could also get a day pass from off the Red Line for
$5.00 then you would have to pay the $1.00 express surcharge
on the 460
(there used be a free shuttle from Disneyland to Universal but according to my sources at Gray line it was cancelled)
and mostly you would have to have board the bus IN Anaheim (no one ways allowed)