There’s a dodgy pen version for PC aye, can’t find anything for Mac though.
InDesign is backwards compatible ONE VERSION – ie CS5-CS4 using INX files, but it’s not the greatest solution. I can see why, with added features and such, but it’s a pain in the behind to say the least.
**edit** Some good ideas there while I was typing! I’ll try copying the install to a pen first and see what happens… I do have a Macbook, but I travel by bike or bus so the less I have to lug around (today I have camera, couple of lenses, flash, bag full of crap for still life and so on) the better!