Need help from expert...!!! networking

Here is my case.. little difficult to explain but i will try my best.
I have a SMC storage device Model SMCWAPS-G to which my external USB hard
drive is attached. The storage device is attached to router [trendnet 54mbps].
i have every thing working perfectly. I can find my hardrive on my local
area network and access file through it. i can play songs and watch movies
wirelessly from my hard drive. Everything is just perfect. i can either
dirrectly connect to smc device or to router wirelessly and can find my hard
drive on my local area network.
all my systems {two desktop, two laptop } are able to access files from the
hard drive. everything is just perfect !!!

My question

1. i am using a soft ware called "limewire" through which i can download mp3
and video files directly to my hard drive.
But when i am trying to download something from the browser for example IE
or firefox the downlond often fails for big files.i.e. 80 to 99 MB
downloads....says "not enough space on drive" !!! while limewire successfully
saves data on it.

2. windows media player can access mp3 and movie files from my external hard
drive and plays them perfectly but how would i set media center in my case
"dell's media direct" to find those files {i.e. on hard drive in local area
network}

3. now what should i do if i want to access my hard drive from out side of
my network... i.e. from my school to my home ????? i know there is something
to open ports on my router but i have no idea how to configure those steps..

I hope i made my point clear enough..

I need an expert brain to help me......is it too challenging??

i shall wait for the Reply...
Thank you.