Most compatible simplest encryptian software

[sswats]

I need an encryptian software that works on all version of windows without needing any software installed and basically just asks for the password when clicking on the drive name.

If it works in Linux even better.
And a Mac OSX alternative please.

Thanks.

 

[sswats]

I run a small computer repair shop, and I backup customers data onto USB hard disks.

So instead of installing software on every PC I want to back up, I just want to put in a password when I plug in the hard drive.

 

[sswats]

because sometimes I finished backing up but I haven't started doing the reinstall so leave it overnight or over the weekend .on our system.

Will try truecrypt out.
thanks