Security implications of having a 2nd boot disk with Win XP

In order to run an old game on my new i5 system, I'm thinking about installing Windows XP on a 2nd HDD, or a partition of a second HDD, in order to occasionally boot into XP to play the game.

On my understanding, this will pose a non-zero security risk to my well-secured Win 7 system, UNLESS I make sure that my Win 7 disk is PHYSICALLY DISCONNECTED at all times when the Win XP HDD is connected within the system.

What I envision is malware infesting the Windows XP HDD while the computer is booted into XP, then having that infestation spread to my Win 7 disk, either while booted into XP, or while booted into Win 7.

Thoughts on this?

 

It would be a good idea if your W7 HDD is disconnected while on WXP if you want total and absolute security for your W7 installation.