Did I understand your question right ?
You wanted to know why you can't find the files from one PC on another PC .

Short explaination :
The Gnutella network is too big for the 2 PC's to find eachother .

Boring Explanation :

The network is decentrialized meaning >

A client connects to another one , thatone to the next , thisone to the next , ... you see were I'm going right ?

Now If you now that a normal client has about 5-10 connections the network becomes allot more complicated . (Imagine yourself a plate of spagethi)

We go back to our first simple chain of clients :
your PC and your girlfrends PC have 11 other PC's (clients) sitting between them .

But on every search you make in a client (Your Gnutella program : LimeWire) there is a max hops variable .
That defines how many clients a search can go trough before the next one thinks it's too old and deletes it .
Suppose this is 10 then our 2 PC's can't find eachother since there are 11 other clients between them .

Let's suppose our PC's would be close enougf to eachother and they should find eachother , Should ...

There is one factor I left out : overload

Imagen 7 clients between our PC's , they should find eachother because the maximum hops is still 10
But there is one smart-*** outthere in that chain (one of those 7 other clients) that has a crummy connection and only a 56K modem (phoneline) but he put's it's number of connections way too high (20 or so) .

His client sees he can't transmit or receive all that data in time and has only one way out : delete some
Now if that happens to be your search it deletes , then the 2 PC's at the end don't receive eachothers messages and can't find eachother .

This is a very simple approuch since there are still some more factors :

Once the search gets whereever it's going , the result to that search needs to come back the same way the search came .
Thus it faces the same dangers as the search did in the first place .

With LimeWire we now have clients and Ultrapeers making things more complicated :
-client has only 1 connection anymore (to an Ultrapeer)
-Ultrapeer manages over 50 connections to other clients and a few(4-5) other Ultrapeers .

That max hop number is in reality allot higher .

There are allot of idiots on 56K outhere that don't know how this thing works (by for example putting up +20 connections) making it suck for everybody .

Now we have a very big plate of spagethi , don't we ?

How do we fix this ?

We somehow force the other guys out and make sure that our 2 clients can "see" eachother .

First let me explain an IP :

An IP is the real addres of your PC on the net , every PC has one (or more)
Compare it with everybody's house having a diferent addres , no 2 are the like .
It's basicly a big long number with a few dots in it like this : 63.211.153.124
Hey if you enter this one in your browser with http:// in front of it you end up in these forums , so you see everything has an IP .
You can find your IP with a tool you download from tucows.com , zdnet.com or webattack.com .
Or with a difficult DOS commando for the Win PC that I can't remember .

In LimeWire you have a screen with connections , right ?
1) Well findout the IP addres of the other PC and type it in here and push "add" .
2) At the same time the other PC must be willing to accept connections coming from others .
On the other PC delete the List with IP's and the autoconnecthosts and kill all current connections .

Catch :

2 has to happen a few seconds before 1 .
How fast can you run between the 2 PC's ?

Now i could have told you this at the beginning but I want you to actually understand what your are doing