use segment to determine which database to use - but how ?

[eluser]cinewbie81[/eluser]
Hi all,

i want to use my 1st segment url to determine which database should i use ..
for eg:

i) www.my-site.com/dell/userlisting
It should linked me to database 'dell' and show me the user listing in dell database ..

ii) www.my-site.com/fujitsu/userlisting
It should linked me to database 'fujitsu' and show me the user listing in fujitsu database

In the link url show above, userlisting will be the class instead of the function .. the segment after userlisting will be the function instead of parameter .. How can i do it ?

Thanks