Different partitions and programs questions

Okay i have vista on 20gb, Xp on 20gb and stuff just for media on a 90gb partition. If i install programs on the media drive will it work in the vista and xp?

 

I guess it depends on the program.
Most will work, but you have to install them twice in the same directory: once in Vista and once in XP. The programs will have to be compatible with both OSes.
Programs that do not refer in their folders to the windows install, or better yey, programs that do not need installation will work right away.

 

Will installing twice in the same place take more space?

 

Of course not.
Or better: it will take the space it needs in the OS partition, because registry keys will be created, dlls will be added (almost invariably to the system folder, as this is the Microsoft way to clutter your hard disk) and registered, a lot of crap will litter your disk as it happens with every windows installation.

You need reinstalling to generate the crap that make windows programs go.
But in the programs partition you won't have more space taken away by this process: you will end up with the same exact folder as before.

Also, I strongly advise you to still keep the more system related apps (such as antivirus and registry defragmenters) in the same partition as the OS.