Newbie questions

[Paul Chung Chee Soong]

Hi. I'm a newbie here and I have some questions to ask :

Is there a limit to the number of hosts allowed in the allow hosts   
directive?
Can I replace the IP address in the allow hosts entry, with the user's id   
(linux user)? The userids will be in the /etc/hosts file.
Can I authenticate using NT Server authentication rather than Linux? If   
possible, any clues to go about it?
User sometimes get hang when connecting with a share directory even   
though his IP address is in the allow hosts list. Why is it so? Part of   
the share directory section are as below:

 [dbx]
 service type=fileservice
 public=yes
 comment=dbx file system
 path=/nfs02/dbx
 writable=yes
 only guest=yes
 create mask=0777
 hosts allow=18,37,17,15, 18.37.17.99, 18.37.16.139, 18.37.16.64,   
18.37.16.97, 18.37.16.200, 18.  
37.16.108, 18.37.16.74, 18.37.17.134, 18.37.16.107, 18.37.17.88,   
18.37.17.236, 18.37.17.245

Please send to my email address as well. Thank you very much.

Paul Chung
(hcsccs at prudential.com.my)