Stefan already said this but you might have missed. What you need is not a separate disk but a partition. Multiple partitions can exists on the same disk or different disks.
PS: While you are at it would you format my vista partition and install w7 there. I have everything ready except the desire to do it:)
Cetin

>Thank you Stefan and Craig
>
>This is all very good news. The new 1 TB HD ( less than $90 from Newegg including a SATA cable and free shipping) is on its way and by Tuesday I should have this installation done. I'll report back here for benefit of lurkers who might want to try this. I'm a big believer in clean installs will a new OS. From what I've done with Win7 RC running in a VM I'm really looking forward to it.
>
>
>>>Thanks Craig and Al
>>>
>>>On further review I don't know what I was thinking re having Vista booted and installing on F:
>>>
>>>I will install the new drive, then set it as boot drive, boot from the Windows 7 install DVD and go from there.
>>>
>>
>>You don't need to, no BIOS settings required - when you insert the Win7 CD and boot from there, it will ask you where you want to install, so that you can choose a partition on your new HDD. If there is no partition yet, you can create it in the same setup dialog.
>>Afterwards, the Win7 setup will install an autonomous O/S there, and will leave the current (Vista) one untouched. And it will create a boot menu that displays when you start the machine, that contains both O/S.
>>
>>IOW, the Windows boot manager will be on the first HDD, but the operating systems that it displays can be anywhere.
>>
>>
>>>Craig - are you saying if I have 2 SATA drives that are bootable, I will get asked on boot which one I want to boot from? If the Vista is drive C: now and when I make the Win7 drive bootable I make that C: in it's world - will the selected boot drive find itself to be C: and the other just get assigned a letter as a slave drive ??
>>>
>>
>>Yes, Vista and Windows 7 are always calling their "home" partition drive C:\, no matter where it is. (As opposed to WinXP, that would call its Home partition C:\ or D:\ or X:\, depending on the HDD/partitions sequence.
>>
>>
>>hth
>>-Stefan