I've been having networking problems for a long, long, long time.
I will try to make everything as clear as possible.
Phase 1: This lasted a long time. I was using my only video card at the time, the 9800 GT, in my computer before I made some hardware upgrades. I had decent overall latency, but the internet would spike to unreasonable latencies every 2-3 minutes while streaming video. I put up with this for over a year. It made gaming much more difficult than it needed to be.
Phase 2: I got my new hardware, including the GTX460. When I first installed the GTX 460, I moved the wireless adapter to the most bottom PCI slot on my motherboard. When I did that, I proceeded to experience the same exact problems I am now: kb/s internet speed, completely dying at times, randomly deciding when and when not to work. After I moved the adapter to its previous PCI slot - one above the bottom - I experienced the decent quality internet with spiking latency in regular 2-3 minute intervals. I put up with this for 4 weeks, until the GTX 460 died.
Phase 3: I switched back to the 9800 GT, my only option. This was exactly the same as phase one. I deleted all the GTX 460 drivers and reinstalled the 9800 GT drivers. However, this only lasted for 2 weeks.
Phase 4: I switched to Windows 7 64-bit, from Windows Vista 64-bit. The video card I used was the 9800 GT. Everything worked flawlessly. Internet was great, no spiking, no bad latency. This phase lasted for almost 2 weeks before the VRAM died on the 9800 GT.
Phase 5: This is where I am now. I purchased a XFX HD Radeon 4650 in the meantime and as an overall budget "back up" video card and am encountering the problems I was having with the GTX 460 before I moved the adapter up to the slot above the bottom PCI slot. This time, however, I am experiencing the overwhelming - not to be confused with the spiking lag - lag while the adapter is in the bottom PCI slot AND in the PCI slot one above the bottom.
** I've done countless power cycles, and have done many hard resets on the router.
** I've gone through 3 video cards, 2 processors, 2 HDDS, and 2 operating systems.
Something to keep in mind about the quality of my internet: it isn't just slow, but extremely inconsistent. It will be 33 kb/s one minute, shoot up to normal for a couple seconds, then back to kb/s. 3 hours later, it won't work at all. 3 days later, it'll go back to working. It's random.
Additionally, I recently reformatted my computer with Win7 again to try phase 4 again, or at least remove all the software/drivers. No progress, unfortunately.
It sounds like a PCI conflict. You've done the obvious -- moving the device between slots. I think I would try accessing the BIOS screens and disable any ports present but not in use -- Game/Midi, COM, Parallel Printer Port.
If any to disable, do so and restart the computer a couple of times to let Windows re-order resources.