Re: Looking for a bike...
While the FAQ above is a great starting place, there's a lot of chaff to weed through to get a specific answer to your question. You're right, a good solid hardtail would be the way to go. At 5' tall, a 13" frame is probably your best bet as are some of the women's designs by Specialized (Rockhopper), Trek (4500WSD), and Giant (Rainier). Specialized and Trek, with their WSD models, actually go to the trouble of specifying forks with lighter springs to work better for lighter weight riders. Lower end forks, like the ones you'll find in this price range, are typically designed for the average 150-160 pound rider and would likely be too stiff for your wife. An air fork would be nice, but you're not going to find one on a bike in this price range. And some of these manufacturers also tweak things like seats and grips to better server smaller/female riders. You also might check out Kona (well built, but generally heavier) and Jamis (great value for the money, though no womens-specific designs).
Just about anything you find in this price range will likely be a little on the heavy side. Going up in price will get you better (read: lighter) components, but the frames will all be essentially the same within a given series of bikes (e.g., same frame whether it is the base Rockhopper or the Rockhopper Pro, just a different color). Start looking for end of season deals as some of the 2007 models are just starting to trickle out. And as the aforementioned threads are sure to mention, be sure that the bike fits her well and that she is happy with it. If something "just doesn't feel right", then it isn't. There is only so much that can be adjusted (seat, stem length, etc.) at the shop. The rest boils down to whether or not there is a "connection". Don't underestimate that. And also don't be surprised if that solid hardtail becomes an entry level full suspension in just a year only to lead to a really nice lightweight, high performance ride from the likes of Titus or Santa Cruz the next.
Good luck and happy trails,
Looking for a bike for my wife. She is about 5' tall. A Santa Cruz Juliana would be ideal; however, were looking to spend under $600. A solid hard tail will do. Any sugestions???