Why is it forbidden, to use our old original Xbox HDDs with the new 360 Slim?

This should answer your questions.
At the end of the day this is MS's service, you agree to the rules they set down or you risk a ban.

If you are found to have put a HDD from an older model 360 into a slim then you risk not only your console and profile getting permanently banned. Also legal action could be taken against you.
A more detailed explanation is available in the link above.

Sorry Grey, that answers nothing. That's also ridiculous. In the future, we have to throw away our PCs if we want to replace a graphic card...

M$, that are bad manners...

It is entirely your decision on whether you want to purchase a new xbox or not.  However, if you do you will have to purchase the new hard drive.  I have 2 xbox's and have no problems whatsoever with getting the larger hard drive.  If you have a problem with the cost, do like I did and watch for sales.  I got my brand new 360 S with 250 gb hard drive for only $130.

[quote user="Bandoleiro"]M$ pushes us to throw away working hardware and spent money for the 250GB HDD.[/quote]Extracting the HDD from the original 360 casing is not a simple task. It also makes it that much easier to tamper with the drive.[quote]First of all, the price is ridiculous, far away from reality.[/quote]The street price for the new 250GB disk is about $100. The price of a new 250GB 2.5" disk is $45. The price isn't "far away from reality" when you take into account that the drive comes pre-configured from the factory with the necessary partitions and security data.[quote]The second point is, that most of the people don't need 250GB.[/quote]Then buy the 4GB console?[quote]What is the statement from Microsoft?[/quote]You mean the second sticky from the top of this forum, Older harddrives, S-model consoles, and ToU violations ? That statement?

[quote user="IceStorm III"]

[quote user="Bandoleiro"]M$ pushes us to throw away working hardware and spent money for the 250GB HDD.[/quote]Extracting the HDD from the original 360 casing is not a simple task. It also makes it that much easier to tamper with the drive.[quote]First of all, the price is ridiculous, far away from reality.[/quote]The street price for the new 250GB disk is about $100. The price of a new 250GB 2.5" disk is $45. The price isn't "far away from reality" when you take into account that the drive comes pre-configured from the factory with the necessary partitions and security data.[quote]The second point is, that most of the people don't need 250GB.[/quote]Then buy the 4GB console?[quote]What is the statement from Microsoft?[/quote]You mean the second sticky from the top of this forum, Older harddrives, S-model consoles, and ToU violations ? That statement?

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The URL was broken, I fixed it. Older harddrives, S-model consoles, and ToU violations