This is from the guild wars site. "Am I required to buy the expansion packs to continue to play Guild Wars?

No. Every purchase you make in the continuation of the Guild Wars saga will be your choice. If you purchase expansion packs you will gain access to new regions of the world, new skills and abilities, new items, new professions, and much more. However, if you choose to not purchase a chapter, you will still be able to play the chapters of Guild Wars that you own, and you will have common areas in which you will be able to play with and against your friends who have purchased the other chapter(s)."

"Will I remain competitive if I do not buy the expansion packs? Will I be able to compete with and against others if I have only some of the Guild Wars chapters?

Yes. Purchasing the newer chapters of Guild Wars will not make you strictly more powerful. You will have access to many more strategic options, due to the expanding nature of the skills, abilities, items and professions that you enjoy with each chapter. It would be similar to building a deck in Magic: The Gathering™: The more cards you own, the more different playing decks that you can choose from to use in the game. When you buy the chapters of Guild Wars, you will acquire a larger collection of skills and abilities from which to build your skill set, but you will not gain more power. So if you purchase a chapter and your friend does not, you will still be able to play competitively against and with one another."