Ronin

Uhm, no.
90% [edit: not really clear at all, what do you mean with external?] no, if you want to be more sure:
Start>run>"dxdiag">"[Return]">Save all information>open Dxdiag.txt>post

Other than that:
You would partition one disk into at least two partitions if you want to install 2 different operating systems on it.

You can only install one OS in one partition, so each partition you make, can be used to install an OS into it any time you want (hence becoming a "system partition").

It is highly recommended to only install windows into the partition you assign the letter C too; That has you running into possible issues, if you want to install 2 windows versions on your system.

Use C for the one you are more likely to end up using regularely.

About master/slave biz:
A) Master and Slave devices only are for IDE hard-drives, which are very old tech by now, it's likely that you don't have those at all.

If you have one removable disk and one HD in the tower, the removable can be only be connected via
- USB [no master or slave disks exist]
- Firewire [no master or slave disks exist]
- eSATA [no master or slave disks exist]
- IDE connected docking station (You would know; To make the drive more hot plug compatible (meaning avoiding your box randomly refusing to boot half of the time), you'd better not set it to the same IDE Controller as the Disk that you have your system partitions on though, lol.)

In any case if at any time your setup has worked, do not mess it up and it will continue to do so.

B) It has only something to do with how the HW bus addresses the Hard disks, it's completely irrelevant to concerns about partitions or what OS you use; Just make sure that the Disk the OS's should be put on is master (I don't know anymore if this even matters though and I am leaning towards the opinion that it does not, but I can't really remember this from the years back in time).

@Old data from a different system:
Assuming it's both IDE-drives and you hook both onto one cable, just hook the one on master, where you want to put the OS's on.
(The cable has a master and a slave tag on it, the not completely ancient drives configure themselves automatically to the position they are connected at, but if they are, you hvae to set jumpers, according to the documentation of the drives, which you hopefully have at hand.)
Swaping HD's between ports they are plugged in leaving alone other PC's is likely to give you issues.

Any HD has a bootrecord in it, that identifies it and helps the system handling it correctly when booting up.
This bootrecord stores informations of where it belongs;
If it gets placed in another system without formating it, this causes confusions, up to the point where the drive hinders the box from booting at all, even after you removed the disk completely, because the bootrecord of other disks get messed up too.

Getting back the data on the disks in this case is a real bother.

If you do not connect them via one cable:
Just plug them in with a cable that fits the connectors, never use 2 different power source connectors, in case the HD features to different power-plugs, if one is IDE, just put it on master, look if there are any jumpers to set and leave the slave position free.

__________________