PITA Internet Connection Problems!

[Feuer Frei!]

Ok, here's the deal:
I am in a house and am using wireless internet.
The modem/router is downstairs, and the account is not held by me.
All i do is give the lady d/s $20 per month to 'tap' into her internet account.
Anyhoo, the connection has been getting worse and worse over the last 3 to 4 months, with the internet dropping out more and more frequently.
At present this crap is dropping out every 15 to 20 minutes approx.
What then happens is that someone has to go d/s and reboot the modem.
A minute later, all back to normal again. For 15 to 20 minutes.
Now, we have contacted the ISP and they give the usual bullcrap down the line, saying to check the modem and if we have another modem to use.
Well, a few months ago the lady did buy a new modem.
We are currently using another modem, her son's.
Both work, in so far as both allow access to the net.
We have also put in a brand new line as well, from the modem to the box under the house which connects the external lines, which lead to the telegraph poles.
Hasn't fixed the issue.
The funny thing is, when the net drops out, i open browser and nothing. But, my torrents are still d/l?
What the heck?
I can't use the net and browse but my torrent is still d/l?
Obviously data is still flowing through, but i can't use the net.
Weird?
Any ideas, guys?