Where exactly is your problem?
How far did you get with the hints I gave you:
http://www.8052.com/forum/read.phtml?id=70671

And Erik's tip:
http://www.8052.com/forum/read.phtml?id=70690

What exactly do you mean by "increment" here?
Originally, you said, "from 12 onwards to 65000"
Do you mean you want to count: 12, 13, 14, 15, ... 64997, 64998, 64999, 65000?

If so, all you need to work out is how to increment by one (this is usually taken as the default meaning of "increment") - and then repeat it as many times as necessary!

In this case, you shouldn't even need the multi-byte arithmetic code - it's just a simple matter of incrementing the least-significant byte, and handling any carry into the most-significant byte.