Is there some software to measure Internet speed and show where the slowest element is?

I use OpenSuse 11.1 and KDE although Im happy to set up a user using Gnome.

Just recently my browsing speed dropped to almost nothing ...I used http://www.broadbandspeedchecker.co.uk/ to measure my speed and it gave a very slow result 30kb/sec ....usually its around 3000kb/sec. I rang my ISP's helpdesk and they told me my ADSL connection was fine. Two minutes later it was back to normal! Hmmmmm
I know the internet speed varies from time to time ...I guess depending on how many are using it and for what. But..
I suspect that my ISP was restricting my speed and Im looking for a tool that will tell me which part of the internet is the "slowest"

I would also welcome pointers to information about internet speed and what causes it to change.

Ive looked at other posts here ..they recommend mrtg and gkrellm. I cant see how they would do what I want..which is to try to locate the "constriction".
Thanks for any help

What kind of adsl are you using adsl or adsl2 or vdsl ?
Using the telephone line ?
If so where is you're splitter and modem located .
What did they promise you a possible maximum speed ?
Or a minimum speed ?
Yes download speed depends on the server from where you are downloading .
Sometimes it helps to give you the speed back by resetting you're modem
Speedtest.net claims that they also can determine the quality of you're connection.

Hi Ron thanks for the reply
answers are..
adsl2/2 down my phone line
I connect via a DrayTek Vigor2800 series to my ISP This is a combined ADSL modem Wireless router and switch. My personal computer is wired to the switch.
The ISP quotes "Up to 8000kb/sec" Im within 1/2 a km of the telephone exchange as the crow files .Im in the UK btw.
Ill try speedtest.net ..this gives me the same sort of result ...approx 3400kb.sec

But speedtest.net also has a pingtest it gives a indication how good the connection is .
I am on the telephone line too .
As they advice me I put the Splitter directly there where the telephone line comes into my house .
From that point it splits the line in a standard telephone line and the line for the modem router .
From the modem router with is placed directly by the Splitter goes HUB line to my LAN .
If I do it different it can cost me speed that is what they told me .
I lives 2 km from the telephone exchange and get 6.83 Mb/s
My provider said max I can get 8 Mb/s it is ads2 too
I get it as Do IT You're Self package
I live in Netherlands BTW