Network activity stalls

Question

I've searched to try to find these symptoms mentioned anywhere else online, but to no avail, so I decided to post here. I have a Powerbook 12" G4, 1.33GHz, 1.25MB, that will stall all network activity from time to time, and it's getting increasingly worse. I've eliminated everything I can think of to isolate the problem. It's plugged directly into a High Speed modem now through an ethernet cable, firewall on, bypassing the wireless router. The problem persists. I think I can safely say the problem is in the Powerbook. Whether it's a hardware or software problem, I just don't know. Oh yeah, I've tried using it on two networks, two different ISPs, using two different modems, and the problem persists.
Before, when I was surfing wirelessly through the Airport card, I found that turning Airport on and off (menubar) would often work, but not always. Now that I'm hardwired, I'm leaving the Network Preference pane open in order to hit "Renew DHCP Lease" whenever it stalls, and that works most times, but not always. It will "usually" fix itself if I wait long enough. (BTW, I've hit that button 3 times in the last few minutes while surfing discussions.apple.com. It's like the Powerbook has temporarily forgotten where the net is - amnesia)
Observations:
* Sometimes, not always, the CPU useage pegs at 100% while it's stalled. (What's it doing?)
* Non-apple software, that might be contributing to the problem, are the aggregators I've started using. Apple's own ITunes is the one I use for podcasts. Democracy Player (video) and Vienna (newsfeeds) are the other two. They send out multiple requests simultaneously during a refresh. I've witnessed downloads, in progress at the time using another program, completely stop when I do a refresh with any of those aggregators. I've seen the network stall many times, using ITunes too, and the feeds time out instead of refreshing.
* I'm using Firefox for the web. As mentioned, it will stall while surfing regularly. Some files downloaded with Firefox have stalled, and they do NOT resume the download afterwards. I've had to start them over again.
* BitTorrent usually works fine all the way through a download, as long as I leave it alone. However, I've watched aggregator refreshes kill torrent downloads that were in progress, cutting connections to all peers. I don't think BT is causing the problem, but it is being affected.
I reinstalled the system a few days ago (archive and install) and then updated to 10.4.8 through software update. It stalled two times while downloading those updates too, while the computer was NOT attended. Sigh. The half-finished downloads did NOT resume, they had to started over from scratch.
I don't know what else I can add to this.
Hitting "Renew DHCP Lease" while it's stalled, will often "unstall it" and then it finishes what it started. But not always.
I want to reiterate that the stalls are not entirely consistent, that sometimes everything works fine. It's just that the problems seem to be related to these actions, like there's something that's not quite up to the task, not every time. That's how it seems to me. It's frustrating.
Suggestions, comments, and confirmation from others with similar issues, would be welcome. Can anyone suggest or point me to a fix?
thanks
Powerbook 12" G4, 1.33GHz, 1.25MB Mac OS X (10.4.8)
Powerbook 12" G4, 1.33GHz, 1.25MB Mac OS X (10.4.8)

Answer 1

Update:
2) I pulled the Airport card and cleaned the contacts
with a pencil eraser and reinstalled. Then I noticed
the power plug has a flange on the centre pin that
compresses. I took a butter knife and spread the
flange contacts apart, just a bit, and then plugged
it in. (The thinking being that the centre pin
contact was too loose, and therefore, possibly,
unable to power the card under full load
conditions.)
Update 2:
Well, I'm 99% sure the procedure above solved my network dropout problems while using Airport (wireless). I mistakenly called this plug the power plug, when apparently it's the antenna plug. Whoops!! It worked out to the same difference though. Poor contact from the centre pin was reducing the card's effectiveness. It's rock solid now.
My other network problems turn out to be related to the new ISP. I think their modem is flaky. It's a 30 day trial, so I'm returning it and getting a replacement. I've been surfing problem-free with the old ISP, now that Airport is fixed, but the new ISP (modem) is still giving me many network problems, that completely disappear when I switch back.
For anyone interested, I'm testing Rogers Portable Internet (available in Canada). It's an early version of WiMax and it looks promising. I recently read where some hotels are charging outrageous small fortunes for conference room net access. This simple device could literally kill that as a profit centre. Just plug the modem into any electrical outlet and you're online. It's 1.5 Meg down, 256K up, and at about the same price as regular High Speed dsl or cable. That's not too shabby. (...if it works as it should.)