I too wanted to do this.
I am stuck at the following step.
Using Getif and the second last option MBrowser I obtained this entry
' enterprises.220.127.116.11.1.1.0 ' and on selecting this entry (amongst the many such obtained) i got this OID as the associated one
I added this entry using the "Add to Graph" button on this page. Now on the last option Graph page, i am getting a graph listing the number of users connected in 5 sec intervals.
Now if someone can convert this info into some more meaningful graph and also with a history........