first - you dont NEED 2 computers, but it helps.
Best option for single computer is to get a dual core (or more than 2 cores if you can).
You will want 2GB of RAM or more (4GB is ideal - more is always better).
Then install blockland like normal, make sure it works. Make sure you can host normal servers with little or no lag to you.
Then goto where blockland is installed, edit (or copy) dedicated.bat and change it use whatever map you want. Then run it.
Start blockland like normal and connect to your own dedicated server (if you sort by ping it will be at the top of the list).
Load whatever you want, and wait for people to join.
Lastly: DONT TURN OFF YOUR PC. if you do, the dedicated server will go down
Can somebody explain to me why you need two computers for this to work well?
most of the PC/laptops used by blockland players can barely run a single copy of blockland. If you run a dedicated server, you will be running 2 copies of blockland. One for the dedicated server and one for your own to play like normal.
Now if you have a dual-core or better PC, then you can probably handle running both a dedicated server and normal blockland on your PC at the same time.