Dual Boot / Shared Software question

[Canadian in Berlin]

What would be the best way to use shared software between vista and XP? I'm talking using Thunderbird on both of them and wanting all the email information in the same place, and some games I want installed on both systems (while I still get used to Vista and want to be able to play them on "ol' Faithful".

Theres other stuff like that, I don't feel like having to go buy a ton of HD space just to use both OSes. Any tips or tricks? Or does it even matter if the games are installed into vista and thunderbird is just a configuration thing?

edit: another example would be that monster called steam!

 

[gigabyte1024]

http://portableapps.com/apps/internet/thunderbird_portable

Use the portable edition, no installation neccessary.

As for Steam... I don't think that'll work too well.
If your doing all this in both OSes, why are you dual booting?

 

[Demon10000]

I installed Steam on XP, then installed it to the same directory on Vista... it seems to work fine. In fact, it ran fine if I just opened the exe from Vista, but it didn't have all the nifty associations with it, so I ended up reinstalling for convenience.

The biggest problem with games is that they often save data to your my documents directory. XP would be a different directory than vista, so you would either have to redirect the folder, synchronize the directories on startup/logon, or manually move files around -- it could be a hassle.