What should I get (and where from) to play RA2 on Linux?
Get Wine. Wine allows you to run .exe files and consequently lets you run Window applications on Linux. While it's not guaranteed to work for RA2, it's very unlikely that you'd be able to get it to run on Linux using any thing if you can't get it to work with Wine.
On the AppDB page, it is reported to have silver/gold status, which means, it will most probably run fairly well, if not flawlessly. Check out the comments in each.