Yours can unofficially take 6G of RAM if it's an iMac7,1 or 8,1, (System Profiler has that info) Apple says 4G. Crucial has two 2G chips for $50 shipped. If you wanted to go 6G you'd have to get two 4G chips, but the machine would only see 6 of it, and they are $90 each.

Crossover has a 30 day demo, and when you install XP, IE 7, and Acrobat Reader it installs Flash 10. I would try that first, and see how it runs on 2G of RAM before spending any money.

Crossover will have IE and XP as default options, but you'll need to download Acrobat Reader and install it as Other application.

You might want to try Acrobat Reader 9.4 first, according to the Crossover FAQs it is more compatible.