There are a number of them out there, but isn't the product key I presume you got valid? It should activate without issue, unless it has been pirated.
And as for the limitations, I have a copy of Office 2003 S&T that I can activate on a pretty much indefinite number of machines (granted, my license allows for activation on more than one). It has reached a point many times where it won't activate on account of the fact that I've done it too many times, but if I wait a bit (say, a month or two), the timer resets.
The first activation mechanisms (as seen on Office XP and, of course, Windows XP) are relatively simple, and are thus full of idiosyncrasies and loopholes.
Nevertheless, I have read that if MS decides to take their old activation servers offline, they'd release a patch that effectively activates the software perpetually, essentially rendering the whole activation thing moot.