The instructions given by Herr PW are correct. For Vista or Win7 it's not much different.
My C drive has XP, D has OFF, E has Win7.
I put XP pagefile in E. Win7 pagefile I allocate it to C.
To do this you've first to turn off pagefiles in both Operative Systems and reboot each time.
To obtain best performance you should defrag your HD's after turning off the pagefiles.
Why? Because if the HD is defragmented you'll assure that when you create the pagefile it won't be fragmented.
So after defragmenting you can then set your pagefiles. Use custom sized, with the min and max value set with the same value, instead system managed; this way it will prevent from later have pagefile fragmented and scattered along the HD.
In my case with 4GB memory I set man and min value 3071. Usually it's 1,5 times the value of the installed RAM, but I use 3071 because both my XP and Win7 are 32bit.
http://mintywhite.co...physical-drive/
http://www.pctipsbox...your-page-file/
http://www.petri.co....ptimization.htm
A good program to Defragment your hardisk is Ultimate Defrag.
With this Defragger you can fully customized which folders will be allocated in the faster access areas of you HDs.
I advised to read the documentation inside Ultimate Defrag; it will give you a good idea of how the things work inside a HD and which strategies serve you better, according to the use you give to your computer.
Here is the download link for the public domain. I prefer Ultimate Defrag 2008 but this one will serve you well and it's free.
http://jayaprakashkv...functional.html
Now you can pay me a drink.
P.S. I know my English is not the best, if there is anything that isn't clear to you, I'll try to rephrase it then.