In the new laptop I have just bought is installed Windows Vista and, according to the seller, if I change the software configuration, i.e. by installing Linux, my warranty expires. I installed on 40GB HD, connected through a USB cable, Debian 4.0.
The problem is, unless I install either Grub or Lilo on the MBR, changing so the software and losing warranty, I can't boot it, even if I choose, at startup, in Bios, to load from USB.
Is there any chance I can manage to boot those 40GB?

Check with your consumer regulations, in many countries that is illegal. Also check the hardware part of your warranty to see if it is any use to you.

It is also untrue anyway - if your drive is erased by an environmental factor, they will happily restore it to image on the warranty. So you can install linux safely and if anything goes wrong, just erase the drive with a magnet.

Also untrue because you have to be able to install upgrades and software from MSN and third party vendors. This will change your configuration. You will be storing your own data. This also changes your configuration.

I imagine you could even change the partitioning scheme and, while a windows install is present, they will honor their garantee. So you have been fed a big fat pork pie (lie).

For the boot from external... you install GRUB to the MBR of the external drive and set the BIOS to boot first from the external drive.

There are tutorials all over the place on how to do this.

That sounds suspicious. I only believe a very small amount of what sales people tell me.

When you set bios to boot from USB, what happens?
Do you have CDRom on the laptop? If yes then make a bootable CDRom and fdisk the USB drive and make sure it is set as bootable.

You can make windows boot to a grub installed on the windows partition.

As preventing you from making changes to your windows install is preposterous, you should be OK...

Personally I would demand a partial refund for the costs of warranty, as tying your hardware warranty to the software is just stupid.

Install the (Linux) boot-loader to the partition on the external.
Go get EasyBCD (a freebe) to add an entry to the Vista loader menu. Works a treat.

Great!
Thanks a lot.
See you on the next question...

The thing that pisses me off the most, though, is this way of trying to do everything is possible to force people to use MS.

Yeah, I'd tell them to stick it up their arse, and use grub in the MBR as I always do.

However, different people have different requirements.