How to get a list of files that are in use?

[Maciej Podoski <Maciej.Podoski@THEMUTUALGROUP.COM>]

I've got a problem with some memory leaks on our NetView box, I think they're 
somehow related to the GUI as they don't occur when the GUI is down.  I've also 
noticed that the memory allocated to files sometimes jumps by 60% or so after 
having been stable
for a day and am curious if there is an AIX command which will tell me what 
files are open and how much memory is allocated to each?  Is there such a 
thing?  I'm running AIX 4.1.5

Thanx