Vista requires much more room than XP. Not only for the OS but for shadow
copy files and such. I have a 750GB C: drive for Vista x64 and not an
unusual number of programs at all. Disk space usage went to 160GB within a
week and has stayed there since (two months). 110GB is allocated just to
the file system stuff like restore points, shadow copies, and the MFT. 15%
of your diskspace will be used by the OS almost from day one. Obvioulsy, if
you have a 100GB drive, only 15GB will be used by the OS for shadow copies
and such, but with Vista more is better so I would use the larger drive.

If you are starting fresh always install the older operating system first.
In this case it is because Vista knows all about XP and how to set up the
dual boot configuration. XP never heard of Vista and has no idea about
Vista's boot configuration store and would simply overwrite it. So you want
XP on the system first.

"Iplant" <Iplant@discussions.microsoft.com> wrote in message
news:A545A40C-C7AB-4D82-AFCD-43D89908DC6C@microsoft.com...
> Thanks Colin...I'll save that for future reference...no PCI slots...only
> AGP.
> I do have two hard drives in this PC one 80 and one 250. I'll just
> continue
> to use the external drive for web building, backups and music.
>
> Now another question...I have XP and Vista on the 250 partitioned drive (C
> and E) The smaller drive is just for backup(D). When I get the full
> version
> of Vista should I install it on D and kill the 5744 version from E or just
> re-install XP on D and format C/E so that it will become all Vita? In
> other
> words...who goes first onto the larger drive?
>
> ---always learning
>
>
> "Colin Barnhorst" wrote:
>
>> An external hard drive needs to connect to the PCI bus, not the USB bus,
>> in
>> order to boot a Windows OS. I use external SATA drives connected to SATA
>> ports on the back of my test computer. I booted Vista all through the
>> beta
>> this way because the arrangement is equivalent to having additional SATA
>> connectors on the mobo. I beleive that the same arrangement works with
>> scsi
>> drives as well. USB drive enclosures cannot be used in the same way.
>>
>> "Iplant" <Iplant@discussions.microsoft.com> wrote in message
>> news:244A395C-64DC-41CB-8B5F-7B53671504A9@microsoft.com...
>> > sorry...I recently purchased a W/D Book (250) external hard
>> > drive...seems
>> > to
>> > work great on XP but Vista is now very slow to boot up. The screen is
>> > black
>> > for a good 20 seconds before loading. Does anyone know why? Anything
>> > I
>> > could adjust?
>> >
>> > Also; I am curious, could I install Vista to this external hard drive
>> > using
>> > the full version and leave XP installed?
>> > --
>> > always learning
>>
>>