I'd guess the next Office will be 2008 (they're usually one "year" higher than the Windows version). It'll probably launch later this year...although I don't remember hearing anything about it for a while.
I *think* I remember hearing that iWork supports importing/exporting Word documents-pretty sure it does.
You might consider Open Office, which is the big open source office suite.
http://www.openoffice.org/
I don't like the interface as well as Microsoft Office, but the price is sure right (free), and it does import and export MS Office files. Super complex formating may not translate exactly the same, but for most stuff it should be fine.
Personally I'd use Open Office instead of Neo Office. Neo Office is built off (a sometimes outdated version of) Open Office. Neo Office basically builds a different interface on it. It's free, so you can always try both, but personally I'd go with the more mainstream Open Office, which is usually a newer version.
Here are current screen shots of how Open Office looks now:
http://porting.openoffice.org/mac/screenshots/ooo-x11/index-Pages/Image0.html
http://porting.openoffice.org/mac/screenshots/ooo-x11/index-Pages/Image2.html
The second one is in a different language, but you get the idea.
I'm not sure if high school students qualify for an educational discount or not, but I'd check that out on Apple's site, as you may be able to get hardware and software like OS X and MS Office for cheaper (Office is like $80 versus whatever it normally costs).
*technical stuff you can safely ignore* Open Office currently doesn't use OS X's Aqua graphical system, but rather the Unix x11 (which is integrated into OS X really well). Practically speaking that pretty much just means Open Office looks a little different from other OS X applications, like it's menu bars are at the top of the windows, rather than the top of the screen.
There are efforts under way to move Open Office over to Aqua, though I don't think they've given a time table (there's a downloadable alpha version). Honestly it doesn't look much different though.
Neo Office doesn't use Aqua either, it uses OS X's Java system to build what some people think looks more like a normal OS X application. I'm not really sure it looks better...but regardless it's an old version of Open Office. (It's goofy those guys are wasting time off on their own thing rather than helping the main Open Office project.)
*End pointless technical stuff*
EDIT: Actually I just checked out the screenshots of the newest Neo Office, and it does look better than it used to. At any rate, you can always try both. Open Office is more full featured than Apple's iWrite, and it's free. I'd think it would at least hold you over until Office '08 (unless you decide to just keep using it to save money). One nifty feature I like in Open Office is the ability to save directly to PDFs, which MS Office can't do.