[TYPO3] Login problem on old install of Typo3.5

[cousins@cousins]

This problem relates to a very old install of Typo3 - if you have had 
experience of managing Typo3 v3.5 then you may be able to help me....

*Problem:* User Login does not appear to work on second domain in pagetree.

*Situation:* one instance of Typo3 source (v3.5), two domains in page 
tree (t.com and n.i.com)
Note: i.com is a static site and not in the Typo3 CMS.

*Apache:* v1.3.33 (Debian GNU/Linux) PHP/4.4.0-4
Apache is set up with Virtual Hosts so that each domain has its own 
entry and so t.com points to /var/www/t.com and n.i.com points to 
/var/www/n.i.com. Server Document Root points to /var/www/t.com/htdocs 
and /var/www/n.i.com/htdocs.

*Typo3:* source resides in /var/www/p.i.com - this source drives three 
typo3 systems (T3a,T3b and T3c each with their own MySQL database) such 
that in this instance of t.com and n.i.com a request for n.i.com will 
first go to n.i.com where the .htaccess file redirects the request to 
t.com/T3b/1.html or for anything other than n.i.com (e.g. 
n.i.com/2.html) redirects to t.com/T3b/$1 [All this works as it should].

*Login:* There is a login on t.com that works perfectly using Better 
Login plugin (newloginbox v1.0.0) on the Login page. Create New Login is 
handled by FE Admin Plugin (v1.0.2). Although an identical setup exists 
on n.i.com (create New Login page, Login page and user database) no 
action appears to be taken when a user logs in on n.i.com (valid user 
and password).

I'm stumped... I've only recently needed to set up user logins on the 
second domain (a club where only members of the club will be able to 
access certain pages - there is no need for the Create New User page as 
Admin will set them up).

*BEFORE* everyone jumps in and tells me to upgrade/use whatever please 
note - the site WILL be upgraded to Typo3 v4 source when the new server 
is installed... if there are instructions on the use/setup of user 
logins on two different domains, I've not been able to find them and I 
have read what I could to ensure the domains are properly set up with 
domain records in Typo3. I am picking the problem is related to the way 
requests are handled in the multiple .htaccess files and or the domain 
set up.