I run an iMac and since I don't do really fancy drawing, I use eazydraw. For 2D work it is GREAT. Easy to use and came with a book to help you learn all the things it can do. It is very easy to use and the author is readily available if you can't find an answer in the book. Also imports and exports to common formats.
If you are looking for an easy to use but good enough for most purposes drawing program for PC, I would suggest the old ClarisDraw program. I used that on my Mac till they "improved" the system so it wouldn't run old programs anymore. Does not import or export, so what you draw is what you use.