files disappearing on mapped drives

i have a strange problem with my netwrok. It is a wireless infrastructure
based network with 2 pc's attached one wired into my linksys wrt54g (v 2)
router and the other is connected via a linksys wusb54g usb adapter. I have
all the lastest drivers and firmware for all my equipment.

Now to my problem.

i have a large amount of mp3's (about 18GB, yes i checked it) stored on the
wireless section of my network. they are grouped into 4 folders all about 3
and a half gigs in size and mapped as network drives. It was originally just
one but the problem concerned reared it's ugly head so i spread the load over
to what i have currently. the files are sorted as follows

top level = artist (folders only)
second level = album name (mainly folders, some files)
third level = tracks (all files)

Now, when i browse through the drives the closer i get to the end of the
drive contents at the third level it start's to lose files until i am
presented with empty folders (this is on the share accessing computer) where
as if i look at the share from the host system all files are present.

Originally i thought that it was a network cache overflow of some kind which
led me to split the intial share of all 18GB into 2, problem still present,
so then i tried my current 4 shares, guess what, still there!!!!!!!!

i need some help on this one and fast please if it is a software issue of
some description can you suply me with intructions to fix it. If it's
hardware tell me what i need. The problem is of such a type i'm starting to
think of investing in some NAS but i'm not sure if that would fix it. any
thoughts???

anyway thanks for your time and any help or advise you can give. detailed
answers and explainations are welcome, if not preferable, as i don't know to
much about networking and i want to learn more and expand my already wide
knowledge of computing.