If you're an aspiring (unpublished, unrepresented) author, buy a PC. Why not a MAC? Because agents and editors (with very few exceptions) want your manuscript in .doc format. "But Pages exports to .doc," you say. "I can write in a Pages file and then just export to e-mail the file, right?" Wrong!
Pages is a great program. In my opinion, it's better than Microsoft Word and Open Office combined. And Microsoft Word for MAC? Probably the worst word processor in existence. Don't even bother with it. Ever. But I love Pages, and I write in Pages because I bought a MAC. To send my work to agents who request pages, I still need a PC. And here's why you should spend your money on a PC if you don't have an agent yet:
If you write in Pages, you need to export to a Word Document and transfer it over to your PC, load it into Word, and then format it for submission. Formatting the margins with proper headers, footers, and page numbers is quite easy in Pages, but the instant you export the file to .doc, it destroys your work. The margins shift, your headers get cut off, and sometimes you add or lose actual pages, changing the final page-count. That means you put together the work of formatting, then you send it out to an agent, only to look like a one of those people who can't follow directions. Sure, in the best case scenario it won't ruin your chance of gaining representation, but if you have ANYTHING going against you before they start reading, it could color an agent's opinion of your writing.
So if you need a new computer, buy a PC, format in Word before you write page one, and save yourself a great deal of time. Besides, PCs are cheaper.