Automatic ppp ip address assignment

[Timmy]

Dear All FreeRadius 2.1 users,
I can run successfully with pptpd and freeradius 2.1 authentication very 
well.  I need to assign ip address to each pptp user manually.

However, I can't set up mysql ip pool for pptp user.  I have tried this way:
http://wiki.freeradius.org/Rlm_sqlippool

but it doesn't work.  ppp user cannot get ip address automatically.  I 
also comment out main_pool inside the /site-available/default file.  
This doesn't work neither.  I have also tried any possible combinations 
of other settings but they don't work.

Any user would like to post the main setting of a successful automatic 
ppp ip address assignment through mysql ip pool?

Your help is highly appreciated.


Your Faithfully,
Timmy