Ok well your ping times looks great the only other thing I could think of why you are slow is this. Do you know how far you live from the central office ,or a remote terminal? the further away the slower you will be.. If no call the isp up they should be able to tell you
Also put your network card in 100 full duplex mode Try turning the modem of for about 10mins see what happens aswell. The link is a guide on how to change the duplex. One last thing try reinstalling your network card drivers ,or see if there is a more current one at the manufacture's site.
http://ots.iit.edu/network/windowsxp_fullduplex.php
These are my settings of the Intel Pro 1000 GT. So far I find, I use the latest last driver.

There is also any difference to explain. I have a fibreglass connection, which means it is not shared like cable/dsl and there is no infleunce in distance from the central office like cable/dsl
I also tried your last settings, but I do not know what happend but after a reboot my PC was going very slow. Also tried to open speedtest.net, but after 2 minutes the website was still not opened. So I imported the first settings you advised and reboot again. But still no progres. Its only getting worse.
@Dannjr, sorry for the confusion, but have no SDSL. It is a fibreglass connection with the same downloadspeed as uploadspeed. So like SDSL. I live in the Netherlands. May be this gives you more info
http://www.reggefiber.nl/Default.aspx?pageID=40