thanks for the very quick reply.
i've never seen it before either. i was able to borrow a laptop and do the test. laptop was on win7 though. anyhow, the issue didnt happen on the win7 laptop, but the speed was nowhere close to advertised speed. at most, the fastest recorded download on speedtest.net was approx 21mbps as opposed to 35mbps that was advertised. this was on wired connection. wireless fluctuated a lot, but i didn't see anything over 20mbps on wireless.
i still can't rule out the laptop being the issue as i've connected my laptop on faster connection and there was no issue.
vista tells me that i have the most up to date driver for the nic. but to be sure, i went to the nic site and surely enough there was a newer driver version. i updated and unfortunately the issue persists.
nic: broadcom netlink gigabit ethernet
as you mentioned, it appears that the nic or something is choking on sudden large packets. one thing i noticed that's different from the win7 laptop is that when the download test starts, the pointer needle on speedtest or the speed, doesn't spike up like on my laptop. for example, on win 7, it spikes to 25 and then hovers at 25 then slowly decreases then hovers then goes back to 25mbps. on my vista laptop, the moment the download test starts, the needle spikes almost to the red zone (like it was shocked), then it goes down quickly to about 20-30 range then slowly and gradually goes down until the connection dies. i'm not sure if that was something to do with the issue, but that's the only thing i've noticed so far.
not sure what the rogers tech would do besides make sure there are no 'interference' on the line like what tech support said. at least i want to see the advertised speed.