Help, I need to upgrade my computer which means I need to go to a new version of my CS2 Indesign, what version can I buy that will open my old files.
The current version is CS6, and that's waht you'll find in legitimate reseller channels. You may find an older version someplace like eBay, but be very careful as there are a lot of restrictions on license transfers and not all licenses are eligible.
In theory, all versions of ID from CS2 onward can open your existing files. I recoomend, though, that you export them from CS2 as .inx files and open those for the most trouble-free conversions.
Do I need to go with 6 or would 5 or 5.5 be better, I really don't know if I need to go with the most resent anything will be better then 2 I guess the machine I am probaly getting has Mac OS X 10.6 snow leopard
Given the difficulty of finding and earlier version, and the new features in CS6 that might be of use to you if you decide to move into publishing to mobile devices (and improved epub export), you'd have to be getting the earlier version at a real discount to make it worthwhile.
Creative cloud is a subscription service. For about $49 month (if you subscribe by the year) you get access to all of the programs in the Creative suite, and some additional stuff, and you get any patches/upgrades as they become available. This is far less expensive than buying an upgrade every year to one of the Suite packages on a conventional license, but more than upgrading a single product. It's definitely worth considering, and may become the only option in a year or two if the market accepts the subscription model.