How to change (Dynamic) IP address in Windows 7 or Vista?

Had same issue on Vista, upgraded to Win7 and issue remains.

I have a Dynamic ISP IP address, yet it remains as if it were static, everything that use to work in XP and previous versions of Windows no longer works in Vista or 7. I spoke to my ISP (3 times, 3 different techs), they said my IP is dynamic and confirmed it is not set by them as static. They charge more for a static IP, so would not just be giving me this "upgrade" for free. They had "no idea" how to force/change a new IP address in Vista or 7.

PLEASE! Do not bother suggesting to run ipconfig /flushdns, /release, /renew at a prompt to do this like every internet search suggests, THIS DOES NOT WORK. This was done with cmd prompt opened under "Run As Administrator".

PLEASE! Read everything I have already done here before suggesting something I've already tried or have tested and proven to work/not work.

Here are other things I have tried, THAT ALSO DO NOT WORK:

(NOTE: no router is being used, direct connected, CAT5, PC NIC to broadband modem)

-Left modem unplugged 72 hours. No change

-Had ISP send me a new modem. No change

-Uninstalled Network adapter. No change

-Changed IP4 settings from "Obtain Auto" to a made up forced IP, rebooted, then changed back to auto. No change

So, with all of this "old school" stuff already tried and failed, what have they changed in Vista and 7 that seems to keep even Dynamic IP's as static? Where is Windows caching or storing this information so I can clear it, none of the traditional methods work. I absolutely can not stand having a static IP on my home computer.

If you internet search this exact question you'll find what I have, everyone is suggesting the once working methods I've already tried above, yet people using Vista or 7 are repeatedly finding this no longer works.

Here's some more information, that confirms the IP isn't being stored in my modem, or assigned to the MAC address of my NIC...

If I boot this same PC to a LINUX Live type CD, using the same MAC address and NIC it obtains a different IP address everytime it reboots. The issue clearly has nothing to do with my ISP, modem, or PC in general.

If I hot swap my modem to a different PC, the other PC gets a fresh (different) IP address. If this other PC is using XP I can force the ipconfig /release /renew to change its IP address.

If the different PC is running Vista, the IP remains static no matter what I try unless the hard drive is wiped and Vista is reinstalled, then it obtains a new IP on the PC with the clean install, yet it can not be changed after this happens.

So clearly, Windows Vista and Windows 7 are holding onto IP configuration information somewhere and reusing this information when it detects you are using the same internet provider, WHERE is it being stored so I can clear it?

Thank you so much if you have a working solution and actually know the answer, instead of just reading what can already be found by a search engine and reposting info that is no longer valid like everyone else on the internet is currently doing when trying to answer this question.