The main element of either bringing in a Beagle to a house ruled by a cat or bringing a kitten into a household guarded by a Beagle is to make the introduction a slow one. In fact, each pet should be slowly made aware of the other before they even meet face to face.
Here are some tips:
Whichever pet is the established one should be cordoned off into a room while the new pet is brought into the house. If you will be confining your Beagle, be sure to not give the impression that it is some sort of punishment and if needed, have one family member stay with the dog to keep him company. If that is not possible, do be sure to give him a new toy (or two), a snack and water to keep him occupied.
The new pet should be brought in and taken throughout the house for a good 20 to 30 minutes, being brought to locations that the first pet has left scents, such as playing and sleeping areas. After this time, do the reverse and allow the established pet to smell the scents that the newer one has just left as he/she explored.
Once this is complete, if both have acted calm during their investigations, with the Beagle on leash, introduce them to each other.