In answer to Sweet Tooth's post (see Japanese Garden Forum) about watering, I'm a little hesitant to give advice as I'm not sure what plant we're dealing with yet. As it was referred to as a bonsai tree, I'm going to presume that it is a Japanese garden juniper, the most common plant in the trade. Hard and brittle aren't terribly good adjectives to describe any plant, but the junipers can be stiff and prickly when in the best of health, so that's not enough to get me to pronounce the plant DOA just yet.
Sweet Tooth, when you say you're giving it plenty of water, is it running out the holes in the bottom? You say you're not flooding it, but if you review the pages on this site pertaining to bonsai watering, I recommend just that at least once a week. If you've dried the soil out completely, water will just run off the top without penetrating at all, so give it a good dunk and let it sit until the bubble trail quits. Once a week and regular waterings to keep the soil evenly moist (not soggy) and you're good to go.
Where you buy the plant is important, especially for beginners who aren't yet skilled enough to spot trouble. Reputable garden centers or specialty nurseries, even web sales are far more likely to garner you a healthy, happy plant than any bargains at the big box stores or mass retailers. If it's half the price that you've seen bonsai for sale, there's usually a really good reason. Many times the plant you buy in a bargain setting is a cull from the benches of a big grower looking to unload his less saleable merchandise; often they are diseased or already dead on the hoof and the mass retailer hopes to move them before any problems are apparent. You definitely get what you pay for in bonsai...
My general prognosis isn't great; the window can dry out plants in a hurry and their often near heating elements (baseboard, steam register, etc.) which can be the death of a plant. Japanese garden juniper would prefer a dormant period (see the page on dormancy), so a bright, cool location would be best (50 degrees in bright indirect light). Hope your tree is still kicking (I bend the tip of a branch 90 degrees; if it bends, it's good, if it snaps, it's dead). Scratching the bark away to see if the cambium layer is still green (bright green, not sage green) is another test. If it's a goner, make sure you read the bonsai pages on this site before you buy again to find the right plant for the right place...